Members of the pools can move to another pool or to new pools in an instant if needed. We would need to know the internal pool distribution of hash power. If almost all the power of the pools comes from one miner, then it can be a problem. But these miners are not interested in 51% attacks because they would destroy themselves.

Those are pools, so they’re made up of individual miners.

If any of the pools misbehave, there’s nothing stopping miners there from unplugging and moving their hash somewhere else

See what happened here with OKEx