Well if we take the previous league as an example and ignore reserves (since he can use them here aswell) and Pikachu (since he's in both) and compare to his current team, he does have someone of comparible power for each member
Infernape = Krookodile (he is about to take down Dragonite 1 on 1) seems to be heading towards main powerhouse status
Torterra = Leavanny (Fully evolved Grass) and Boldore (Better tank then Torterra was)
Buizel = Oshawott (similar movepool) and Palpitoad
Gliscor = Pignite (both started weak Tepig lost a lot and Gligar was a crybaby, then became instant powerhouses with an evolution, Pignite might well evolve soon too)
Staraptor = Unfeazent, both fully evolved birds
Gible = Scraggy (Both come off as the weak babies of the team, yet pack a huge punch)
So not counting Ash being able to use a lot of reserves, including his actual Shinnoh team, his Unova team seems to be shaking up nicely compared to it. Its mainly the starters that are falling behind, but that doesn't take away the fact that through Krookodile and Leavanny he still has 2 fully evolved Pokemon just like he had fully evolved starters in Shinnoh.
Also if you compare by the time he got 8 badges (Pure Pokemon from that region, no Pikachu since he's on every team):
Kanto: Charizard, Squirtle, Bulbasaur, Pidgeotto, Krabby, Muk & Tauros (30x)
Johto: Cyndaquil, Totodile, Bayleaf, Noctowl, Phanpy
Hoen: Torkoal, Corphish, Groovyle, Swellow, Glalie
Shinnoh: Infernape, Buizel, Torterra, Staraptor, Gible, Gliscor
Unova: Pignite, Oshawott, Snivy, Scraggy, Unfeazent, Krokorok, Palpitoad, Boldore, Leavanny
So going by evolutions while on his team,
Kanto he had 2 evolutions, and 2 fully evolved Pokemonand 1 Pokemon (well 30 of them
) with no evolution
Johto he had 1 evolutions, and only 1 fully evolved Pokemon
Hoen he had 3 evolutions, and 2 fully evolved Pokemon and 1 Pokemon with no evolution
Shinnoh he had 7 evolutions, and only 4 fully evolved Pokemon
Unova he has 7 evolutions, and only 2 fully evolved Pokemon
So when comparing to past regions he isn't doing that bad in terms of teambuidling, its mainly his starters that are falling behind, but he has far more reserves who are doing fine and evolving nicely (though not given enough screentime)