At which points do you believe Ash NJ Team surpassed his Sinnoh, Kalos and Alola Teams?
Here's the way I consider the PWC tiers relative to Trainers we've witnessed in the previous regions.
World Champion Tier
: Leon (Significantly >>> Anything we've seen in the previous Regions)
Upper Master Class Tier:
Cynthia/ Steven (Significantly>>> Regional Champion Cynthia, Steven and all Regional Champions we see in the previous series).
Mid-Master Class Tier
: Diantha, Alain, Lance (Slightly >> Regional Champion tier we've seen in the previous series).
Master Class Tier
: Iris, Raihan, Flint(Regional Champion tier of the past. At this stage you're more than capable of being one of the strongest trainers of a Region and strong enough to be among the best in the world)
- Hyper Class Tier : Drasna, Volkner, Bea (High Elite four tier compared to previous regions): I would compare trainers at this stage to be relative to Elite four members we've see in the previous regions (Flint Aaron, Bertha) and also Alain with MCX only). So technically, I'd rate current Volkner to be ~ Previous Sinnoh Flint/Bertha etc).
Lower - Hyper Class Tier:
(Strong enough to hold their own against an Elite four member in battle): Tobias, Kukui with Tapu Koko, Brandon (Full Power)
To me reaching the Lower Hyper Class tier means you're more or less strong enough and very likely to win a traditional Regional League. This makes sense as the person who wins a traditional Regional League would then potentially challenge the Elite four.
That said, Ash had to overcome an even bigger Obstacle to enter the Hyper Class as Iris was a Regional Champion. I'd argue Iris at this point was between the Upper Hyper Class Tier - Master Class tier and Ash had to be at this level to beat her.
So in other words, Ash was already significantly capable before entering the Hyper Class which further explains why he rapidly reached the top.
Hence, in conclusion, I would argue Ash's Journey's team more or less reached his previous Regional League team status between his Great Class Battles; from around his rematch against Bea.