These are not playoff systems for a championship but for a promotion/relegation. There are better examples like the Belgian league but they carry over more benefits from the regular season.

The champions league determines the teams going the brackets in 8 "season" games. Instead of > 30.

But even in your bad faith argument the number 1 and for the championship even the number 2 is decided by just the regular season. So they understand that the regular season should mean more than some seeding.

Everyone knows that in 80 games a half are either walkovers or don't mean anything in the end. They are only there for the money and could be cut for a better league. They could, just like 3 pointers, even make it a more profitable option.