Though, the problem with "gradual changes" is that the tyrants can easily adjust for them, relentlessly attack them, and eventually corrupt and capture them. By your argument, unions demanding fair wages and sane working hours could make a difference, but they leave the same monsters in power who bit by bit find ways to erode the power of any gradualists trying to compromise. And now it's hard to say unions accomplished anything at all.
You can't compromise with bullies. They just keep pushing it.