it kinda just depends on how well the story is written. some dogshit, low-effort storytelling where some immature dickhead has a magic dick? jam in as many "love interests" as you want. a well-written harem with an actual plot and well-fleshed out characters? usually, i think the best would be if it limited itself to like 5, maybe 7 at the most. there are exceptions (see: grandma's house, despite the criticisms) but they are few and far between. i genuinely feel like the harem trope is more often or not just a way to fit the preferences of more potential players into one single story (the giga-stacked goth, the lithe tomboy, the shortstack tsundere, etc. pick your favorite type!). could be laziness, indecisiveness, or even just efficiency on the part of the author. i mean, look at the never-ending discussions on who the "best girl" is in certain fandoms. those discussions don't happen in non-harem media (usually). in my most earnest opinion, the absolute best way a harem plot can be done is when the "main" girl gets off on the mc pumpin loads into other women right in front of her. having a genuine cuckquean as the female lead is peak harem beyond reason.