There's no doubt a rape tag is needed here. Consent can't be given by someone whose mind has been altered by you. That's the same as getting them drunk and then having sex.
But the no consent is already in the mind control tag and they do consent to the sex after having their minds altered, so the actual forcing happens in the mind controlling part.
It isn't the same as getting someone drunk, as consent isn't given or at the very least it can be taken back after sobering up.
I am not trying to defend mind control, it is an evil act (unless you have consent), but in terms of story and feel it is different and likely evoke a different response in people.
For me personally I don't see the rape tag as being right here, as the game don't have any instances of sex without consent. Let's look at it practically. Let's consider different types of people based on their likes:
MC+rape+ - would likely be disappointed in a rape tag, as they probably enjoy seeing people being forced against their will
MC+rape- - Would likely turn away from this game, because they don't like seeing people being forced, therefore they would likely miss out on a game they would like. I fall in this category I like MC, but don't like people being aware and against it without being able to stop it. Again I know in real life it isn't better than rape in any way, but I don't control my kinks.
MC-rape+ - Likely wouldn't play this game at all, unless they really likes rape and they will be severely disappointed
MC-rape- - Won't play this game.
Who exactly would benefit from the tag?
The only ones I could thing of would be people okay with mind control as long as it isn't used for sexual reasons. Seems like a very niche group to me and they can probably figure out that this game isn't for them even without trying it.