Personally, I feel like 3–4 LIs is a bit too few, so 5–6 is my sweet spot! Something like 4 standard LIs plus a locked character who unlocks after clearing everyone else—making it 5 in total—feels perfect and doesn't give me burnout. I love it when each LI has a best, normal, and bad ending, and then there's a true route that opens up after hitting all the best endings.
Once it hits 7 or more LIs, though, it just feels too overwhelming to clear them all lol. Of course, having a huge roster means a higher chance of finding your specific type, and there's definitely that 'buffet style' fun of picking and choosing, but still...!