Bro it's clear that you don't understand what a fantasy world is it's going to have different cultures and beliefs is societies are going to be a lot different from Earth it's literally the whole point of fantasy and isekai is Peter being transported into a different world or watching fantasy...
It's clear that they had high expectations or you just dropped it really early but I do understand your feelings about trash manga and how lazy they can be with their writing especially with the overpowered MC and with the izakai genre but I wanted to give you my point of view about this manga...
Well one it's a bit too early for the main character to get a harem just yet cuz one he was weak two he was not comfortable with dating multiple girls at once and three she was open for the idea for him to have multiple girls around him she just wanted to be his only wife I could go into more...