I don't play the Sims so it's hard for me to have an opinion on it, but games like Overwatch, Call of Duty, and pretty much every BR have all had copycats and clones, and none ever succeed.
*if* someone could make a superior product to PokeMMO there'd be an argument to make, but either nobody wants to because it's a small market, or nobody knows how to. Even when I look at the other Pokemon MMO's, they take all of the things PokeMMO does well, and go in the opposite direction. 3D graphics, non-canon storyline, no breeding system,, no GTL, extremely easy shiny rates, etc. Nobody has attempted to take what PokeMMO does well & improve upon it.