The principal team of Ash is:
Pikachu, Pignite, Oshawott, Snivy, Scraggy, Reserve.
You see that none of this most used pokemon are fully evolved.
Ash has this team now:
Pikachu, Unfezant, Oshawott, Pignite, Snivy, Scraggy, Leavanny, Boldore, Palpitoad, Krokodile.
Ash needs this league team:
Pikachu, Unfezant, Oshawott (you like DSewott but marketability), Emboar, Snivy/Servine, Scraggy, Leavanny, Seismitoad, Boldore/Gigalith, (trade and back), Krokodile.
I think for best and worst to prepare for the league:
Pikachu, 8.
Pignite, 7,5.
Krokodile*, 7.
Leavanny, 7.
Oshawott, 6.
Snivy, 5,5.
Scraggy, 5. (it's a bay, I don't expect in a equal leel in the League anyway).
Boldore, 5.
Plapitoad, 4.
Unfezant, 3,5.