Mea culpa. In my defense, though, I never released a NSFW game before, and last time I checked, which is to be fair quite a while ago, there was no way to flag a game as NSFW besides the tagging system (remember that itch is a very young site and it is constantly changing). Also, the flag is not on the main page of the game page creation, it is hidden in the metadata menu and you have to know it is there and look for it (which I didn't know until it was mentioned to me). Which is why I put the CW in the beginning in the first place, since I don't want to expose people to content they don't want to see.
You say CW is not enough, but to me it's actually the best way to approach this, since if someone happens on my game by chance, surpassing the internal filtering system of the site (like from an external link), they will still know if they want to play it or not. I mean, you can't get much better than having the dev itself say "look, this game has this and this, if you don't like this then don't play it." But I can see why it isn't a good choice to enforce CW at the beginning of every game.