The usual standing order for Biolab fights is MAX, Medic, LA, and engineer, with Heavy Assaults specifically being called out to switch to a more useful class. I think leaving Heavy Assaults out is a mistake as they provide a very useful counter to something we struggle a lot with: NC MAX units. When playing on my own, I take out NC maxes all the time as my primary kit (HA). Drop a rocket into them and they're quick to finish with a LMG. When in Biolabs I switch to MAX (if it's up) or one of the other requested classes, but I feel a few HA would go a long way to countering those MAX crashes we get from NC. Vanu MAX units just can't stand up to the sort of firepower that NC MAXes can bring to bear (they can drop my MAX suit, even with 4/5 kinetic armor, before they need to reload if they're running hacksaws). Granted, MAX suits of our own are very important in Biolabs due to their durability (and thus the supporting Engineers and Medics) and control of the roofs is crucial as well, but I don't agree that HAs are without a role in these fights. Rockets annihilate MAXes (75% of their health in one shot unless they have flak armor, which is around 50%) and oftentimes can take out their supporting engineers as well. High capacity magazines also help in sustained battles. Also, as an unrelated PSA: If anyone finds themselves defending in the Biolab (especially in areas like the generator room), please do not stand in the doorways! Standing in the door only insures that A) Enemies can shoot you and B) Friendlies also can only shoot you. You've effectively become a meatshield for the attacking forces. If you step back 5-10 feet, now a dozen people can easily bring their weapons to bear on the MAXes as they come through.
It's super situational but it depends largely on what you have certed. If you have C4 on a LA, go LA. You can one shot a max. If the team needs muscle and you don't have C4 on your LA and don't have anything unlocked for the MAX but you do happen to have full nano, upgraded shields, an upgraded launcher, and some extra grenades on your HA, then I say HA is the right call, but that's a lot of caveats because .... You also don't need any certs to make good use of the medic or engineer classes. If you're a heavy and you're respawning in the room instead of getting a revive or going for resupply instead of standing on an ammo pack you're probably doing it wrong, especially if the MAXes are dying and can't get a revive either. If there's plenty of support on hand, the team needs muscle, and you're certed for heavy but not LA or MAX, then heavy is fine.
