Carrying Helii on a Myrmidon is about as unrealistic as fitting a Boeing 747 in a jeep.
That said, on Insane it's a nightmare to fly on a Myrm; the only flaw (and it's a major one) is the large target profile. Anything else, it actually excels at, with decent firepower (more than Herc II/Ulysses), average speed, okay hitpoints, fine secondary loadout.
Terran Mara of course, hands down. Super-Fighter. Period.