If downvoting, an observeable action, does not change behaviour, how could the knowledge that someone could ignore my content change it?
But reporting content for not being marked as adult will change behaviour or there will be trouble from Itch.
I just scrolled through 30 pages of most recent assets. I have found no explicit adult content. "Best" was two female low pixel models that had no clothings. But those were neither explicit nor adult in nature. Open a project in a new private browser window next time you encounter one. If a warning appears, it is marked as adult and your account was configured to see these things. Adult stuff also appears, if you use any of the "adult" tags. Those were recently removed from the tag suggestion box to prevent accidentally selecting them.
As for the overkill, if a dev has one "bad" and one "good" game and I happen to see the bad game first, ignoring the dev forever is the overkill. I can just as well ignore the project. It is just a key stroke. Ignoring one or ten projects is not much difference.