Attack helicopters, armored fighting vehicles, and I believe the Marines still have their own tanks.
That's the point, yes: an "armored fighting vehicle" is just a substandard tank that stands no chance in a "real" fight. And that's by design, not merely because General Motors would be poor at building tanks for Marines or something. It's the tactical intent that these vehicles should steer well clear of battle, and settle for hauling troops to fighting locations and then giving some firecover. Leaving out any actual armor or armor-piercing weaponry is a good thing in increasing mobility and carrying capacity - but also in discouraging the AFV commanders from trying to engage heavy enemy vehicles in battle.
Ditto with the helicopters of Air Cavalry. Not even the purpose-built gunships are viable vehicles for fighting their peers; they deliver firepower, but they are designed to avoid actual fights, except against grossly "asymmetric" targets.
Which makes perfect sense. Forces intent on deploying and supporting infantry should have no business taking part in battles against actual fighting vehicles, because that would be senseless endangering of the infantry to no real gain. Vehicle forces capable of fighting tit-for-tat in turn should have no business providing rides of infantry, not for any significant length of time anyway.
and I believe the Marines still have their own tanks.
True enough. And the M60 is undeniably an actual tank, rather than a mere armored fighting vehicle. But whether the presence of tanks in an opposed amphibious assault is justified is something military history is yet to prove, as their use so far has been limited to unopposed landings and disastrously failed raids. Once the Marines are past the beach, it's time to let the Army in with its much better (read: heavier) tanks, so...
Incidentally, what would be the best equivalent of a tank in the Star Trek environment? Would there be any benefit to, say, a vehicle that is incapable of flight or spaceflight? In the "taking the beach" phase, or in the "beach taken, bring in the actual tanks" phase? And what dramatic aspects should be considered here?
Timo Saloniemi