I agree with Gebel. It's all in the execution.
In the real world, actual harems exist with cultures that have male-dominated polygamy (hello, personality cult leaders and Mormons though some say they do and some say they don't do that anymore), unfortunately, almost all of them offer more interesting dynamics than what you'll see in a webnovel. The issue is often that the author either just isn't good at character writing, or they'll be cranking the wish fulfillment up so high that as soon as the harem members become an official part of the menagerie, all of their personality, drive, and ambitions will shrivel up because they can't be allowed to clash with or limit those of the MC. I know it's a harsh accusation, but a good study of this effect can be seen in Virgil Knightly's
Monster Girl Sanctuary available right here.
Essentially, harem MCs have a nasty tendency to either become faceless projections or
black hole sues, and the second breed is arguably worse because those stories may actually improve by simply
removing the MC.
The easiest way to boost your harem novel is to make the relationships bumpy. Have the girls disagree or even fight with the MC and each other and don't resolve said fights in the same instance that they occur, and don't use "fake" points of conflict secretly designed to make your MC look good (he's just too loyal, so of course he yelled at her! ((this is actually the kind of logic real-life abusers use, and is an interesting angle for unreliable narrators or problems that the MC has but can't see, too bad many authors don't use it)) ).
If you really want to make your harem look like a living, breathing anime ecosystem, give your love interests personal desires that they can accomplish without the MC. Does the cute witch want to free the soul of her sister trapped inside a voodoo doll? Have her go through the shonen power cycle in a separate thread and let her achieve her goal in a way that makes her look awesome without the MC, even if she has to separate from the party for a few chapters. You could even
have her lie to and use the MC despite her feelings for him/her and damage their relationship in a way that requires the two to actually do some adulting if they want to patch things up with each other, but don't make her regret saving her sister (the MC isn't the most important element in the story to her, the cute witches' sister is) and damn any reader that says the MC shouldn't have "kept" the cute witch, if love can make the women stupid and forgiving, it can make the MCs that way as well.
TLDR, just make your goddamn harem love interests actual characters instead of blowup dolls, it's not that hard!
Alternatively, if you want to show multiple females getting the Long Slchong McTong TM just have them roll around with no strings attached without the need for the MC to "lock down" their bedmates. People have casual sex all the time.
