Maybe I missed the point, but I have a good tabletop experience with VTOLs of a speed of only 7/11 or 8/12. This normally allows a minimum engine and maximum free weight for weapons and armor. You have always modifiers of +3/4/5 and make quite difficult be hit.
You don't get much experience against players who also field VTOLs, do you? Try it sometime. Also suggest trying it against opponents fielding LBX, HAG, and flak ammo. there's a big difference between "I'm cool and fast because I'm the only one here" and being genuinely viable across multiple eras. (I've humiliated Hawk-moth drivers using the humble Ferret, rendering their long-range support fire moot by denying them the ability to cruise and keep a facing on the enemy, and the Jellowbucket...er, "Yellowjacket" has been a great way to distribute gauss rifles as salvage ever since they removed the "Explodes on crashing" from the rules.)
Keep in mind, those numbers come without changing elevation or facing. (both of which cost MP, neither of which contribute to TMM).
9/14-10/15 is a baseline cruise because of that two-point rotor armor plus rotor facings STILL being the majority of your hit locations. Even with the munchkin damage reduction, something like a Mantis will EAT your bigger, slower, gunships, and LBX pellets don't get damage reduction without using Ferro-lam. (remember, you take damage when you fall, and you fall if you lose your motive system in a VTOL. In the old days, you also exploded.)
upshot being, 7/11 to 8/12 is really only viable if the other side is comprised of energy boat heavies that don't have a lot of speed (Player skill being equal. you can kick the crap out of a Noob in a Widowmaker using an urbanmech if you're any good.)
of course, this all relies on standard or 'book' designs. Outliers using experimental tech and edge cases really don't count for general purposes, aka if you need more than the basic rules for the unit type in TW/TEchmanual to make it work, then it's a bad design unless you're also allowing for the optional rules that hinder it.
(which tends to mean most of your combat turns will be spent looking up pages to win arguments instead of playing the game.)
In
General terms, 9/14 is the new standard, because the rules provide JUST enough cover to make that moving eight hexes with a turn at medium not suicidal against a mixed force in ANY standard era (Star League, Succession Wars, Clan, Jihad, Dark Age).
keep in mind, the damage reduction and "Doesn't automatically explode on crashing" was done to make the Jellowbucket (Yellowjacket) remotely viable instead of the rather poorly timed joke it began as.
The hawk-moth is only viable because of the incredible reach of it's primary weapon, but it's quite a trick to NOT wind up stationary from a fire-support position while still remaining in range to support your ground units, and it's helpless against another VTOL, and crippled against fast 'mechs, hovers, or anything that can put up a similar movement curve because of the weight restriction.
The best "General Purpose" VTOLs (viable against other VTOLs, capable against headhunting Hovers, light 'mechs, and clan units) tend to have some basic traits;
1) minimum of 9 cruise.
2) weight range between 21 and 25.
3) 2 weapons-a long range and a short range, with at least 1 capable of crit seeking or applying secondary effects.
Examples:
H-7 (3026, not the 3039 nerf) -AC/2 for long range plink, SRM-4 for delivery of Infernoes (Third succession war to 3039), AC/2 capable of using specialized ammo (3050s-3060s era), with Inferno delivery.
Viable against: Other VTOLs, enemy units with LBX support (meaning it won't die as easily and can cruise at speeds other units have to flank, thus avoiding becoming one with the terrain on a psr while still being able to canyon-carve.)
H-8 (TRO 3058) LRM-5, SRM-4. Infernoes for the SRM, your fave flavor of LRM munitions for the LRM rack.
Viable against: Other VTOLs, units with LBX support, good against Vehicles, superior to H-7 against other VTOL units except when Precision ammo is in use.
Cavalry AH (and variants): while the main version is somewhat hampered by its armament, it sports a highly viable movement curve and excellent Inferno delivery or crit-seeking for removing other side conventional units.
Mantis: Excellent against other VTOL units, good scout.
Ferret: If you're play predates the 3050's, this is still a good chopper-hunter and spotter able to 'canyon carve' (screen behind terrain) without being an easy target when the map isn't cooperative.
Marten: less capable against other VTOL units, but a good platform for delivering Inferno rounds onto infantry stands and vehicles, good spotter, manueverable enough to actually use terrain as cover/concealment.
H-7 (tro 3039 version) while hampered to make the Donar (TRO 3058) look good, this is still a very effective vehicle hunter, and is only seriously hampered against faster VTOL units.
Donar; the reason they nerfed the H-7. This was the premier Clan chopper, at 9/12 it was meant to be a Warrior on steroids, but in match-ups tended to lose to H-7s in fights despite having significantly more firepower. that one MP of movement actually, in experiments, proved to be something that matters in BMR era play. The streaks make it only good for crit-seeking, without the ability to deliver infernoes, and the main gun (a Clan energy weapon) is an excellent hole-puncher, giving it one of the nastiest alphas on the map for the tonnage and speed. Good for fighting Inner Sphere medium 'mechs and opponents who don't know what an LBX autocannon, Flak ammo, etc. are.
Pinto: overweight but still effective, best used as a 'slick' for carrying infantry and dropping them off before raising hell with the enemy's flanks. The crit-seeker here is the LRM rack, but that limits you, and may be better used to deploy smoke to screen landing zones, than as an actual weapon. the medium laser is effective as a 'holy crap' punch (as in "holy crap I need to shoot that tank before he kills me!") adequate speed for the infantry mission, adequate speed for using terrain to screen an approach, even adequate against other VTOLs. probably one of the better units to choose if the other side has heard of anti-air weapons like LBX cannons, or is fielding VTOL units as well, since it can actually dance. (10/15 on a 30 ton chassis, it's still very limited, but is the heaviest of what I consider 'viable' combat VTOL units.)
These are the units I've found to be most effective in actual
play, as opposed to theory crafing where the assumption is a completely flat map with no terrain to accidentally run into because you're forced to flank.
remember; sideslip with VTOLs only happens when you're exceeding your cruise MP, and when it does, you tend to discover that clever 'screening behind terrain' results in deconstructive lithobraking or (more frequently) being completely out arc to fire while presenting your juicy side profile to enemy fire at often ridiculously bad ranges for you.
Mediocrities:
Hawk Moth. This unit has enough range to stay out of combat, and enough speed to make it difficult to stay out of combat. best used against Urbies, 3rd succession wars Annhilators, or anything that can't move very fast and has a max range of 15 or less.
Outright BAD designs:
Yellowjacket (the worst). the only viable version is armed with Arrow IV, and that's only in the off-map artillery role. it's too slow to survive and too juicy a target not to be belle of the ball the second it pops up-while having the same innate fragility every other VTOL in the game does. This unit is superb for delivering gauss rifles and expensive armor plates to the other side as salvage, but absolute garbage for anything else.
Cappellan "Stealth" armored Warrior variant with the self-detonating cannon; this unit has one weapon, with ridiculously long range and a 1 in 36 chance of exploding when you fire it, thus gutting the airfame, killling the pilot, and crashing the aircraft-even on a miss. There is literally not enough bad that can be said about this...thign from TRO: experimental. it's a design that would never have gotten past the first engineering student to look at it in-universe, and if it got past them, it wouldn't get past the first COMPETENT officer in the CCAF to look at it.
Sun-Tzu did not develop his rep by hiring morons. Clearly this is the result of some legacy people from Romano's tenure who haven't yet managed to get fired, or it's a success of MIIO in industrial sabotage. (Heck, it might a success of SAFE, or any other intelligence agency's efforts...) if you see it on the other side, smile, you're either up against someone who doesn't know what they're doing, or up against someone who wants to hand you an easy win.