Yeah this MMO debate is silly and sounds like it comes from someone who has never actually played or understood what a MMO is.
Letting eternal characters affect seasonal progress is just not what seasons are about. Seasons are meant to be like a wall between the two. To progress the battle pass, you're meant to do new activities and seasonal objectives with new characters, conforming with new mechanics and gear. They've literally designed their post launch content around seasons, they've been upfront about this aspect. Expansions are a wholly separate thing coming, but before that new stuff is coming in seasons.
I understand how one might think it's just okay to let the season pass progress through old characters, but it's not even structured around that and doing so would warp it. I would be surprised they budge on this since it undermines the seasonal experience for those who want that type of experience. And they've designed these seasons in advance so pivoting might not even be feasible even if they felt it desireable. I am sure they're taking in all the feedback, but this isn't feedback on seasons. To get actual feedback on seasons, they need to get into people's hands.
I watched that video where the guy reacts to the reaction. All he is doing is staying dug into his opinion that his way to play the game needs to be supported so much that it affects everyone else. And it's simply based on his perception of what things should be. He can do what he wants, level to 100 on every character. No one is stopping that. But he wants to take away from the seasonal experience, which would absolutely happen (although it's not obvious) because they would need to warp their system to allow for this.
They've been clear you cannot buy power in the battle pass. But that doesn't mean there isn't power and advantages in the battle pass. They've been super up front about this all, that battle pass has power but it's part of the free tier. And you actually need to level up to unlock certain benefits. How is it fair or even desirable to negate that level requirement wholly? It's there for a reason, that reason being a level playing field for seasonal characters.