How do you feel about natures? There are 25 of them in total, but for almost every Pokemon, only 2-4 of them are viable. Even then, many Pokemon strongly prefer 1 of those few, and having anything else might actually be hindering said Pokemon? Espeon, for example, would really appreciate Timid, is also cool with Modest, and doesn’t hate Calm or Bold even if Espeon doesn’t get much out of them. Any other Nature either doesn’t grant any benefits at all, or actually hurts Espeon.

I feel like natures work the way they do at least partly as a result of their interaction with generation III’s contest mechanics, which failed to survive in most of the later games, and in that respect they’re sort of emblematic of the way Pokémon is now composed of a whole bunch of legacy systems that no one is quite willing to get rid of.  I don’t think you would design natures the same way if you were creating that system from scratch in generation VII without reference to things like the five contest stats, or berry flavours.  Some discussion of what you could do here, here and here.