I guess I'll use myself as an example. I'm pretty much focusing on a fire pool and I practically use only that against every other element besides water; I have an earth team that has an okay pool for water.
Once I finish my fire team, I can pretty much just stream roll Tiamat no problem, and then after that use a wind team to fist Yggdrasil and so on and so on.
So with at least 1 mono team that's strong you can do pretty much anything they throw at you; however, if you don't focus on anything you might end up weaker than if you just focus on one element.
It might not be a bad idea raising pools evenly to some extent, because for some bosses debuffs barely ever hit unless you're using the supereffective element. Plus, you'll take a lot less damage and be able to survive longer.
Not sure if any of the mods still support this community, but they should be aware that the forums are infested with bots and that their forum needs to be upgraded.