You mean turret bastions. Tank bastions spawn on a timer after the 1st orisa is killed
Most groups I've jump in with agree clearing the turret bastions first is the best route. Came close again, pretty sure the optimal strat is to VERY quickly rotate around killing turret bastions before getting the 1st orisa.
But the tank bastions are an absolute nightmare. Usually you'll find yourself finishing the 2nd orisa with about 2:00 on the clock. Very soon after, you're faced with a new wave of shield bots, the final 2 orisas and their shields, plus a tank bastion. That combo seems unbeatable, I can't see a way to beat that combination of enemies w/o all ults AND somehow no shields being up AND torb's level 2 turret SOMEHOW being alive in the perfect spot. Your tracer will be down before she can dismantle the shield bots shields, and your rein's shield is toast soon after.
The group I played with had 1 person who cleared it already, and we subbed in another random who also cleared it, but with me on torb our dmg output was never ideal