By that logic Bea is the new alola champion
1. Ash won the regional Alola league. Although I could argue the Alola regional league is much inferior to the other regional leagues, let us simply assume it is the equivalent of a regional league. That doesn't really mean as much. While it does look like a big achievement primarily because Ash never won a regional league, the reality is that regional leagues constantly happen and a lot of people keep winning. For instance, back in Hoenn, Ash could've very well beaten Tyson, the Hoenn Regional League Champion if he used his reserves. That said, Tyson is no where close or even on the same level as Steven who is a regional champion. Since Alola doesn't have an Elite four/ Regional Champion, we can't simply declare Ash as the equivalent of a regional champion. This would be like saying, since you came first in your school football tournament, it is exactly the same as winning the FIFA world cup.
2. If there was a legitimate title on the line, there would have to be an official battle. Like for starters, Ash didn't use his main Pokemon when he fought Bea for the first time. This would be different if this was a supposed Title defense. He simply used newly captured Pokemon. Plus, Ash is by no means referred to as a champion tier trainer. If you recall, Leon referred to him as an unrefined trainer with a lot of potential at the start which indicates that Ash is still far from being Champion Tier like Cynthia, Steven etc.
Plus you misunderstood my logic. I'm not saying Ash should be better than all his opponents. This is the pwc after all. For all you know, there might be a lot of trainers in the Great Class and Hyper Class who might have won regional leagues in the past. All I'm saying is Ash's Pikachu simply cannot be weaker than Goh's Cinderace. This simply demeans the plot. Goh is a rookie trainer who isn't even keen on battling.