Arthur Morgan is the GOAT character ever.
This argument could have also been applied to Iris, before JN065, so no, it's not applicable.In hindsight, it kinda makes sense. Paul was always not really very strong, especially considering his core team of Pokémon got entirely swept by Cynthia. That’s not to say he couldn’t have improved, but I can also see why he likely isn’t on the Champions’ level.
If Ash can be considered Champion level now, Iris can be bumped up to that level with no explanation, then so can Paul.