This is probably why they created the polygamy tag, because too many harem don't go anywhere. To be honest its a pretty "recent" trend to actually have polygamy. Up to the early 2000s, Tenchi is literally the only harem I can think of that ended in polygamy. All other harems ended with either no resolution or one girl picked. Then all of sudden you got DxD, Strike the Blood, Muskou Tensei, etc. and polygamy endings became more than just Tenchi, so they started using the polygamy tag.
But yeah I no longer bother if it has harem w/o the polygamy tag to follow.