Greninja, can use the Bond Phenomenon, trained Lucario (who is awesome on its own), for all we know it may stack with Dynamax and Z-Move? Unfortunately has better things to do in Kalos than participate in Masters 8.
Lucario, went from hatchling to one of the strongest Pokemon in the world on par with two of Cynthia's aces super fast.
Gengar, also capable of Gigantamax and had some good battles.
Charizard, now this is probably an unpopular opinion, but I believe it never got the chance to show a power ceiling. Consider that given the correct tools, it has the versatility to go into Mega X, Mega Y or Gigantamax. We just have not seen it yet.
Next up, I would say Dragonite and Dracovish, both very strong Dragon types, one pseudo one super unique species with great typing and interesting signature move.
Another unpopular opinion, but before Sirfetch'd we probably have Infernape. I just think it is Ash's best Fighting-type.
Also rather unpopular opinions, but Goodra (also pseudo) and Sceptile (fully evolved starter) may actually be very strong. Maybe the Sunglasses Krookodile, doubt Ash got anything better in his Unova team.
From that point onward, there are several fully evolved ones or just not-evolving that are all OKish but nothing special. Especially all the Flying types. Yet also stand outs like Snorlax, Heracross, Leavanny, Donphan, Glalie...
There are a few mid evos like Bayleef, Pignite, Quilava, Palpitoad...
On the weaker end, I would put Gible (too much untapped potential), Totodile, Corphish, Snivy/Oshawott, and worst of all probably poor Scraggy (hatched as a baby and never really trained much).
