Uh, I mean, I could see a 1v1, MAYBE, but not an actual set legion of Sentinels. They copy powers and can send those copied powers to each other, evolve to counter those powers, and can do it on sight, if I remember correctly, because it's all based on scanning and genetic replication via Mystique's abilities granted by her own DNA. Assuming the Sentinels get fast and strong enough to fight at an even level thanks being enhanced by MHA Quirks, or just in a speed equal, I think the Sentinels have an easy chance of wiping out the low tier MHA Cast as a group.
But a singular Sentinel is much more reasonable to handle given they sort of like, focus in on their dedicated counter, and if you can get around it, then it's possible to get them while they THINK they've countered you. They also don't use their power IMMEDIATELY. Instead they chose to fight the Bunker Mutants directly for a bit before they decided to evolve, so the 8-A Cast has time to put them down before they start getting nullified.