Well, honestly, as long as we are talking about it being in a modern setting, most harem manga/manhwa that actually reached completion ends with 1 girl or just leaving it open ended without the guy actually choosing anyone. Rather surprisingly, a modern setting harem manga/manhwa that actually ends with a harem is rarer.
I only begin expecting that to be the ending after the author put various hints of it being the case. I got into reading this at first expecting just one girl is going to win, and I'm sure many did too, there's a reason there's quite a few comments saying they're hoping 'name here' would win and others saying 'even though I know the author isn't going to make her win, 'name here' is best girl, and also 'Da Hee is definitely the one going to win, she's the first girl that MC met at the start of the series', those sorts of comments are seen quite often(especially at the start) because they thought it wasn't going to end in a harem.
Basically, in the end, whether or not you like harem is just a matter of taste, arguing about it is just pointless, no one is going to change the others mind, but I just want to say that I doubt the ending is the ending that everyone expected would actually happen, at least when they first read it.