> I find there seems to be a wall at 2 years after an acquisition.

It's called a vesting schedule. ;)

What I've seen is that usually the founders and heavy hitters from the original company are very BS-averse and basically just stay around to collect their money and then jet for a situation that doesn't suck.

For the rest of the gang, it tends to bifurcate: some folks stay at the big company indefinitely after the acquisition because while they can see the suck, nowhere else pays as well or is as cushy (I know people who have been thinking about leaving for 12 years). Still others excel at big company work and make a happy career out of it for a while but don't stay forever.