(edited after reading the addendum. I thin you could get that 10/15 by dieting instead of XLE, but not with the added armor shown in the H-3 and H-6)
but really, you only need the LRM racks for dropping smoke or thunder-mines (and the second is only in optional rules now), so two five-racks aren't that great, esp. when you've got a back-armor-swatter that does 8 points of damage to a rear arc on anything that you would normally use a VTOL to deal with in direct fire. Minus the bigger engine option, this is a credible design, meaning it's a solid bit of work, again not overpowered or excessive, that makes use of the free heat-sinks of a fusion mill fairly well, and it'll eat the lunch of designs like the Yellowjacket, Hawk-moth and similar fetishized big-gun VTOLs, while having the ability to at least try a return shot against other "hunter" VTOLs in the light range, and better still, it out-performs the Cyrano on everything but raw straight-line speed at 5 tons less and significantly better crash protection for the pilot in the event of a low-altitude interaction with something that shears your rotor off.
I don't favor it as much as your Martlet chin-turret design, as that one feels more like something with a definite role, but it's not a bad effort and not a truly poor design-it definitely has a role it performs well-enough, and the flexible mounting for the main gun makes up for a MP of movement in most cases, giving better combat performance than the Donar has simply on the basis that there are more angles where you can engage with your primary weapon,(Successfully), which means less need for that extra MP to turn while maintaining TMM in flight.
consider putting a light PPC on that turret instead? it's 3 less damage, and you pick up a minimum range, but that's less of a concern when even your secondaries have a minimum engagement range.
