I have to agree with
@Scribe here. And I think that we have to be careful about not equivocating here in your statement. There is a difference between saying "there is a common problem in D&D" and "the problem is D&D itself." Trying to insinuate that people are arguing the latter is potentially inflammatory, as it implies people just hate D&D. I don't think that's the case. There are many D&D Diehards on this forum who have criticized spellcasting and "restrictions" with spellcasters as being too easy in D&D 5e. I don't think that they hate D&D or believe that the problem is D&D.
I don't believe that the issue is "D&D" because "D&D" has throughout time and editions had ways to curb the power of spellcasters: e.g., interrupted spells, AoO, concentration, prepared Vancian casting, armor casting penalties, discovering new spells, different XP progression, lack of at-wills, utility spells as out-of-combat rituals, etc. These past editions are very much as D&D as 5e D&D.
However, these are things that have been increasingly rolled back to make spellcasting easier: e.g., improved HP, neo-Vancian, at-will cantrips, rituals, abilities for regaining spell slots, no armor casting penalties, etc. That's fine, but there has been
relatively little to no counter-cost to spellcasting for what benefits spellcasters have increasingly gained.
There are a number of ways that WotC could curb the on-demand power of spellcasters while still very much being D&D or even without being 4e, if that is your suspicion.