It's not "obvious." The episode didn't even air yet and we don't know if every single Champion of other regions were invited to this tournament, or even if it was only Champions that are participating. It's also not "obvious" that as soon as Alola gets a proper Elite 4 going that Ash would be thrown off his spot automatically because he doesn't "have six Elite 4 or Champion tier Pokemon." These are just facts that you're fabricating when at the end of the day, we know nothing and the writers can make Ash as strong or weak as they please at the snap of a finger. We can't even discern how strong PM 2019 Ash is because Ash has yet to go all out or actually be challenged in a Pokemon battle.
And oh, powerscaling is most definitely opinionated. I don't even think it's possible to powerscale without having some bias in there unless the author actually explicitly ranks the characters themselves with numbers. Case in point, no one can seem to agree whether Greninja is "champion tier" or not because of his showing against Diantha. And no one can agree if Ash's entire Alola / Orange Island's team is "champion tier" or not because they faced off and defeated Kukui's and Drake's team. Similar to how you're arguing that Drake and Kukui are not "real" champions while others think that they are. Or how some people here like to argue that Diantha probably fell out of bed backwards and sprained her ankle and was spiked up on coffee on the day that she faced Ash and hence Greninja's showing against her was a fluke. Powerscaling is doused in opinions.
If there are some champions that won't be participating it's obvious they didn't bother to show up. He wouldn't be thrown off automatically but probably challenge Ash to battle where Ash would get thrown off.
This "writers can do anything" stuff is so overused on this site it's really annoying. Like NSS( no sh*t Sherlock) annoying. Of course writers can do anything. But we're talking about feats and facts that are given to us in the time which proves that current Ash's Pokemon are not E4 except Charizard and Peakachu. That's why I said in other comment that if writers decide to throw in Sceptile, Infernape we will see how strong are those Pokemon, which obviously writers are dodging that. DP is last time we have seen old Ash's Pokemon battle which is 9 years ago. Ash only possessed 3 Pokemon that went in E4 level: Pika, Chari and Greninja.
Powerscaling is definitely NOT opinionated it's based on facts and feats. Powerscaling is not " which battle you like the most or which is the best series". Liking = subjective, powerscaling = objective.
About powerscaling and bias it depends on the users, there are tons of users like me who are neutral who are looking at both sides and episodes to determine which Pokemon is stronger and which level they are. Even if I like/dislike someone more. Example, I like Ash's Sceptile and Infernape more than Peakachu and Greninja but P and G > them, that's a fact.
People who disagree with facts are wrong, obviously. Greninja is not "champion tier" he's more mid-high E4 tier based on Diantha's feat. He made Base Gardevoir evolve, that's a fact which automatically means he's E4 level. No one claimed he was champion tier. Kantonian and Alolan Pokemon are definitely not even E4 tier except said SM Peakachu. Those are all feats and facts presented in episodes and with certain logic involved.
People who think Kukui is real champion are wrong. Drake is stated to be a champion in the anime and that's fact. Kukui is nowhere near stated that he's a Champion, he's just a professor. Diantha= what? Again, powerscaling has nothing to do with opinions, it's all in feats and facts. Based on your logic if someone says that Krillin is stronger than Kefla it's just an opinion, or if someone says that Naruto would beat Goku it's just opinion. Lmao no, they'd be wrong. I hate how people who never had powerscaling debates over years try to act smart and teach people who had powerscaling debates in years and years like me. I lived on powerscaling debates when it comes to DBZ and Naruto and sometimes DC, this is my field, so I know what I am talking about..