Of course complaining helps. If you say nothing, it means you approve of the decision, and then there's no reason to change it.
The problem is if you only complain for a couple of days and then forget about it. For itch.io to seriously consider reversing the change, there would need to be real damage. How? By leaving itch.io, of course. For developers, removing our games and not publishing here anymore. Or at the very least, setting to 0% the share we donate to itch.io from each sale. For players, stopping the use of itch.io or at least no longer buying games there.
Will we do that? Some of us, yes. But probably not enough to cause real damage for itch.io to reverse the situation.
As for what you said at the end, yes, of course they'll bring back NSFW content. What they're doing now is reviewing all games and removing those that violate their recently tightened policies. When they're done, they'll bring back the rest. The problem is the damage they're doing to us, the developers, in the meantime—and the damage to our freedom. They've banned one of my games that doesn't break the rules at all, and they just didn't care.