Well the LGR has slight superior range bands to the AC/2 you like so much for the VTOL "snipe from halfway to the horizon" tactics you advocate for survivability. So 17 hexes is medium, and it hits four times as hard. And 25 hex range, well if the enemy wants to play turret Tech, you can get high enough to negate nearly any cover and have enough ammo to take long range potshots till they move.
It's just the mass of the weapon, over half the whole chopper once you count ammo takes up so much room. You could maybe get the Hawkmoth up to 9/14 with a fusion engine, but have to throw out the second ton of ammo, or go for a fuel cell, which came into the game well after the design. 10/15 requires a XL fusion engine, unless you jump the design to 30 tons, and even then still needs at least a light fusion engine.
Going up to 30 tons actually
slows you down. The suspension factor loses 'sweet spot' between 25 and 30 tons and what you end up with can be done cheaper and better on a hovertank (which doesn't have nearly the pyrotechnics from losing motive that a VTOL does...or did, before they nerfed out that too.)
to push a hawkmoth to 10/15 requires lightweight engines (iirc it already comes with a fusion plant, so you're looking at an XL.) This is a basic problem with the phallic-big-gun philosophy of VTOL design-better designs under the prior conception relied on LRM, or AC/2 for range, because
those allow it to move. under the current regime, the Hawk-Moth is really about the upper limit of useful, and that's more to do with changing how the damage is dealt in an effort to salvage the overweight chopper designs with the overcompensation guns.
you know, trying to make the 'Assault vehicle' choppers worth taking by trying to line them up on the same scale-of-assumptions we see with 'mechs (Heavier is better/more survivable). Basically they had to give them magic vibranium rotors to turn 30% of the hit locations into a shield capable of deflecting everything but specified weapons.
the sick part being, the previous rules were actually
more realistic than the current rules.
small arms can and regularly DO kill helicopters in the real world when the pilots get sloppy or cocky-and most often by inflicting damage to rotors or engines. (because those components have to be precisely balanced and KEPT in balance or they pull themselves apart via centrifugal force and unstable airflow.)
this is all, of course, an argument that's been had before. many times.
the out-of-universe explanation is simply that they were integrating rules from Unbound, Munchtek (maximum tech) and MFUK sources (among others) and wanted to preserve a unit that has special favor with a segment of the playerbase (The Yellowjacket gunship in specific) due to being a contest winner back when we had the OLD magazine (and FASA was a functionally alive entity). There were a large number of players who would refuse to play in games that didn't incorporate Munchtek's Munchkin options, esp. with regards to vehicles, and they were quite vocal about it.
There were some improvements to TW: Sideslip was incorporated more thoroughly, including penalties for flanking all the time, which is good, imho, and applying sideslip to Hovers (which would be the case-an air-cushion vehicle is going to be running on a low-friction surface and doesn't by definition have 'traction' for hard manuevers). but there were, in my view, some rules that should NOT have carried over to the core, and among these, is the rotor-damage-nerf, esp. considering the later incorporation of fancy armors that make LBX pellets a non-factor, particularly since the change to sideslip was sufficient to unseat the savannahswarm exploit by itself.
VTOLs honestly didn't need it, but
specific VTOLs did-because they were examples of 'yes, you can do that, no, it won't be awesome'.
and imho, that was fine. Part of a game that lets you design units, is that some designs even canon designs, are simply going to suck no matter how amazing the concept sounds before you stat it.
NOT every design needs to be a winner. sometimes you get a T-34, and sometimes you get a Vickers Valiant. There isn't a GOOD reason to change the physics of the setting to salvage said Valiant attempt, not when other designs work just fine.
Try running the Goat Path scenario-12 3026 H-7s against a light company of mechs in mountainous terrain using BMR(r) rules-it actually
works like the writeup unless you dump the stats on the choppers to green...trying it at same tech levels with Yellowjackets and you're redistributing armor and in some cases gauss rifles to the winning team of 'mechs by turn 5, as salvage.
This is the true origin of the "VTOLs are too weak" argument. using designs that were actually
bad designs with an impressive main gun as if they were tanks or 'mechs with predictable results.
btw: the tactics that worked for VTOL users pre-TW still work, it's just that now you can run previously garbage designs and get almost as good a result thanks to that 35% immunity to incoming fire presented by the rotor damage nerf. (The reverse is blatantly NOT so. Try running TW era tactics by BMR rules and you'll lose...often quite badly.)
This is kind of akin to the changes to Tank tactics from Total Warfare's adoption of Munchtek rules for tanks- in BMR(r) play, parking was what you did NOT want to do with tanks. EVER. Some designs were only good for a 'surprise!' positioning (3/5 and slower designs) usually one or two turns of fire, and if you wanted win using conventionals (tanks especially) as your primary force, you
stayed in motion as long as possible. why? In BMR(r) play, parking was a suicide act if you weren't also hidden (using Hidden Units rules or double-blind with hidden units). why was this? because there were weapons that were an IMMEDIATE threat no matter how thick your armor was, and by immediate, I mean 'existential' threat.
Infernoes hitting a hex with a tank or two in it meant a survival roll in the heat phase and 'get out if you didn't cook off because you have to make it again'. a single inferno could kill an Alacorn, which made a bog-standard Commando (CM-2D or S) an existential threat to a lance of Alacorns that had to be dealt with-because it could kill the whole lance in a couple of turns if it caught them out without support.
(You ain't gonna do that now. NOW you have motive crit tables that encourage parking and so much of the critical table is motives that you end up having to slowly erode your way through the plating-which is more plating than an equal weight 'mech can carry with the same weapons load due to spread per ton).
this in turn meant that for conventional-primary players in BMR play, you didn't park. You at LEAST cruised every turn, and tried to avoid flanking penalties, which made the 3/5 designs among the weaker options, (Unlike Battlemechs, where being bigger and heavier translated into superior survivability AND weapons load), this in turn required some finesse to pull off, but made it more rewarding when you did.
but it doesn't fit with "park at medium range and roll dice until someone explodes".
In both cases, an Achilles Heel was removed with Total Warfare's adoption of munchtek's rules. In both cases the expanded damage charts mainly added dice rolls and made specific (often narrowly specific) tactical or equipment options that were questionable-to-bad into viable (in the case of the big-gun heavy choppers) or even preferred (in the case of "parking at medium and rolling dice because you don't NEED to move") options under the new system.
In BMR(r) Big, slow VTOLs were worthless BV sinks, in TW they're viable options. in BMR(r) Park-and-turret was suicidal behavior, in TW, it's how you run tanks if you want to win. In both cases, the physics of teh game were changed to make top-weight, previously too-slow-to-be-useful units more useful and more in line with
battlemech play.