I know everything can be used, but it is impossible for everything to be equally useful.
For example, I will compare Spinda to Linoone. Both pure-normal types. Linoone, though, is at least one rank higher in every stat, except Special Attack where they are even. Linoone also has a better movepool, and a better priority move. So, by that reasoning, although both are usable, Linoone would be better, even if just slightly.
I could also compare Vivillion to Leidan, and get a similar result. Vivillion has better stats in everything but special defense. Vivillion also has better abilities and a wider movepool. So, Vivillion is better than Leidan.