It seems each “type” of guardian share the same skill set from their respective database +/- one or two. I think there should be more unique skills among same types. Each guardian may have a signature move that sets them apart from the other ones in their category.
Right now as things are, success comes in picking the strongest skill, then picking the guardian that has the highest stat for that skill. defense, special defense, hp and speed are hardly utilized enough in this game.
Some guardians are rendered useless because of this mechanic, so you basically see the same 4-5 guardians in rotation in pvp. This game has good potential and would like to see it become more :)