What if, instead of an EV cap, there was a total stat cap? As in, “some Pokemon are naturally good at fighting, but all can achieve the same level of expertise through training” taken literally?
I think this has consequences beyond what you immediately intend. For one thing, under this system evolution and higher base stats are a bad thing, because they mean less flexibility – more of your stat cap is taken up by things you can’t change. For another, unless you have some sort of equivalent to the EV system – some limit to how far a Pokémon can advance beyond its basic capability in each stat – you’re going to end up eroding the differences between species of Pokémon. What’s the point of Alakazam if it can push its defence just as high as anyone else can, or everyone else can push their special attack just as high as it?