How many LIs are too many?

[Arisa-chan]

It's too many when some routes get more content and the others feel like sub side story routes. Generally, most games have 4-7 LIs, however there are some games that manage to do 12 like Heart no Kuni no Alice.

In the Alice series case, there was a very short common route/introduction and the meat of the game was visiting your LI to get their endings. It worked well since in the Heart no Kuni game each LI's route kinda explored different aspects of Alice's character and not so much plot was locked in a character route. So it was fine to skip some routes and focus on the ones you love.

Personally, I think that games with 7 or above LIs tend to favor some LIs more. Around 5 seems to be the sweet spot. But, what matters the most for me is how fleshed out each characters' route is. I prefer to have few LIs with routes that really explore their personality and romance than many LIs with shallow routes.

 

[Qroha]

Maybe more than 6?
I am definitely not against many LIs in one game. Sympathy kiss I liked really much despite having a lot of LIs. So optimally 6 LIs max, because the writing is not good when there are a lot of LIs

 

[Arietta08]

I generally would prefer no more than 4-5 LIs. Anymore than that and I begin to get burned out, even when it's a game I'd like to finish. I encountered this issue with 9 RIP for example, where I was having a lot of fun with the game and eagerly binge playing it, but by the time I reached the last couple of routes I could tell I really needed a break.
I don't mind skipping routes that don't interest me in a game, so too many LIs won't put me off from playing a game, but it does still kinda feel like a shame to not fully finish a game if possible.