I think people enjoy the fantasy that Real, Juve, Bayern, MU, Liverpool, Arsenal, PSG could be relegated in the modern era... rather than the reality.
It's like the American illusion that if you compete hard enough and find a niche that you can defeat Amazon or Walmart in retail.
But I suppose keeping that illusion intact would make it much more palatable for fans who actually think the game is played on a level playing field.
Leicester Premier League Champions
West Ham competing for a CL spot
Tottenham suddenly became a CL club
Liverpool won the Premier League - Remember they were hot garbage for nearly 30 years until 4~ years ago.
You're misreading the point when you see "relegation". The point isn't direclty relegation, it's the inability to
not qualify for the competition through success in the domestic league
The domestic competition and the Champions League are intimately joined. Now that is threatened.
Imagine a world where third placed Manchester United who are 7 points behind Mancheter City with 8 games left on the season make the choice to rest players in the league against Chelsea, thinking there's no point in risking injuries for a maybe-shot at going up in the table, because they're placing Barcelona in the midweek in a competiton to qualify for the tournament playoffs in the Super League.
That is the reality you're advocating for. The domestic leagues WILL becomes second priority.