I can understand people being upset with the lack of scaling but ive also notoced i havent seen any concrete ways to balance it all without blocking off progress. There's 3 main story lines right off the bat, and spme people may even do each one one at a time, all 3 at once, or outright ignore some they dont wanna do. Thats not even menrioning the objectives are split unevenly (8/5/5, then final bosses for each line), or that not all pokemon are created equal. If it was steictly badges i could see it but try doing the same with titans and you can see the logic fracture.
Option 1: Level hot swapping. All of the bosses are clearly designed in an "ideal" sequence and the levels follow that. So like. If you want me to do Gym 5, Gym 6, Titan 4, Star 4, Titan 5 then there's no reason that the levels cant update accordingly such that Titan 5, Gym 5, Titan 4, Gym 6, Star 4 don't at least swap their levels around.
Option 2: It just scales on your highest level in the party. We FF8 now. Go nuts. Do all thsoe titans first and now go tackle a first gym that's level like 30 or whatever. You decide to grind up to 100 for no discernable reason and now you go fight Brassius with his inexplicably level 100 Smoliv. Who cares!
Option 3: It soft scales. There's a floor and ceiling that each boss can't go below/above.
incidentally for all of these I am not touching wild encounters or trainers. I think those can stay mostly static, someting you can reliably lean on to make exploration a little spicy &/or safer and can opt in/out of leveling or whatever. Although, I would probably try to have some low level mobs in high level areas so that if someone really really wanted a Cetoddle they could sneak their way up the mountain and find a nice low level one for their adventures
I also think boss teams would probably remain unchanged (the Isle of Armor did this if you did it in the post game). The series is no stranger to throwing under leveled evolved pokemon at you and high leveled smoliv is stupid but in a funny way.