Then you aren’t responding to the argument, you are inventing a new one.
The comment that touched off the reponse, and that you agreed with was:
It IS easy to up the challenge in an « easy » game than to downgrade the challenge in a « hard » game, particularly for the experienced DMs that are more likely to have players that build powerful characters.
What you are saying is that a GM can increase the difficulty, they just don’t want to because they dismiss powerful PCs as « superheroes », even if they exist in a world where all creatures are powerful.
Which naturally begs the question: if the GM’s players enjoy playing powerful characters to the point that the players resist efforts to rein in their characters, why is GM trying to sell them on a game that they clearly don’t want to play?
When a GM sells a game the players don’t want to play, it falls apart. For instance, in a game I was a player in, one of the principal reasons the game fell apart was that the GM failed to identify what the players enjoyed in RPGs. The GM thought the characters would principally be motivated by greed and violence, and was completely taken aback when the party refused to kill people other than in the defense of innocents.