I believe it can be done well, but it is almost never done well.
Most harem stories follow japanese manga tropes.
in japanese manga/web novels, the Protagonist never has the balls to make a move on any of the girls orbiting him
the characters are almost always one-dimensional fuck dolls who exist to boost the main characters ego
most harem stories have no relationship with logic or human psychology
but harems exist in real life too, dont they?
Wanna turn the genre on its head?
First, youll need an ALPHA protagonist. This needs to be an attractive, confident male, that has the ability to sexually satisfy multiple partners.
second, give the women of your story ACTUAL personalities. Maybe they love the MC but hate sharing him & compete with the other girls. maybe they get jealous and try to sabotage the other girls relationship with the MC. Maybe they get into vicious catfights.
Maybe a girl decides that she doesnt want to be just another conquest for the MC and decides to leave, thats right, THEY LEAVE THE HAREM.
Maybe a girl, angry that shes not the MCs #1 girl, gets mad and cheats, and later regrets.
maybe the girls start out hating each other, but slowly open up to each other, and fall in love & have bisexual orgies
Drama, life, emotions. A harem could be a gold mine of storytelling, if done well.
Alternately,
if you are doing a historical or fantasy, where nobility is common, you can have your MC have multiple arranged marriages, to secure a bloodline.
Maybe those wives dont even love the MC
If you are a lady,
then have your male harem fight. men do not share. very rarely will males be okay with other men fucking 'their women'
when your FMC becomes romantically involved with one male, have another one get angry and leave\find another woman- maybe hell still be attracted to the FMC and cheat.
Maybe the FMC realizes at the end, that she has been playing with the hearts of these men and regrets it
MAYBE THE MALE MC GETS TIRED OF BEING SEXUALLY EXHAUSTED AND RUNS AWAY TO LEAD A SLOW LIFE IN A SMALL FISHING VILLAGE!!!!