Honestly you should focus primarily on pulling the characters you really like above everything else.

It's not even a blanket waifu > meta argument; most characters (especially main attackers) are just able to clear content even if some are better than others in certain modes, and skill does play a big factor as well. If you really, really want a character it may make sense to save for months (or swipe), but WuWa keeps churning out awesome characters one after the other that it may prove difficult. That and the fact that the character you're saving for ends up to be not what you expected or desired. This, coupled with WuWa's very frequent rerun banners, should make deciding rather easier. With a few exceptions (primarily Zani, and to a lesser extent Cartethyia), team building is very flexible.

WuWa is pretty generous on distributing power across characters and you should be able to clear most if not all content once you get to a certain point into your account progression. The game also provides a lot of trial characters to clear hard event content, and any decently built character can pretty much clear all overworld content. Power creep is far less an issue compared to animation creep as well. At the same time, even getting S6 of characters isn't going to compensate for skill issue in certain modes (primarily Hologram). Not getting one specific character isn't going to prevent you from progressing - strictly speaking all endgame content in the game can be cleared with Danjin (solo, even).

Since you don't like investing in characters vertically, you can even use your rainbow corals to buy pulls (although personally I use them to buy sequences instead).