Have you forget about Pachirisu in the world championship ? ;)
For me, I won't use a Pokemon under 450 base stats. I know some people who won't use a Pokemon under 500. But a lot of my favorite Pokemon are under 500 lol.
There is a lot of Pokemon I love but I won't play with, like Farfetch'D, Delibird, Dodrio, Dewgong, Arbok, Sandslash, Venomoth, Cherrim (althought these last 3 I could definetly made one some day), Fearrow, Butterfree, Beedrill, Raticate..... a lot more too...
I'm one for giving every mon a chance, and most can work with the right team support. The worst mon I can think of at the moment is Unown. Mons with limited movepools in general fall along my least favorite, but Unown is just awful.
And Lucario too ? Delphox ?Delcatty, Persian, the other felines. As much as I love them in-game, in competitive... no, never.
Abra.
My Glare, Coil, rock slide, headbutt Serene Grade Dunsparce would disagree ;)Dunsparce or Magikarp. Enough said