I agree with this. But it does not discount my points. I can only say that I watch a lot of people play in person and have a large amount of experience in playing with diverse groups. This has been, much like you, over years in the hobby. There are many players and DMs that do not read any of the books. They just build stuff from Beyond. There are even more DMs that have never run an adventure path or written adventure. They just want to do their own thing. And there are even more DMs that have not played as a player. Even older players, who wear the badge of "forever DM" are missing a huge piece of the learning experience in the game by only DMing. The semi-experienced ones that only DM often do so because they found their niche or they found the joys of world building and storytelling. But they are still missing that learning piece. The young DMs that only DM do so more often than not due to social constructs, and those are the ones that probably most need to be a player.Not really.
It more comes down to D&D transitioning to a different type of game at high levels once low level spell slots stop being critical to combat.
When you have 1st and 2nd level spell slots that don't have much damage or range over cantrips, spellcasters transition them to buffs, movement, and utility. And the game changes. Was the same in older editions with auto-scaling spells.
You have to recognize that. This isn't told to inexperienced DMs. It's more more less a "trial by fire" almost every DMs goes though if they play high level play. And few designers and adventure writers write for the change of play. "You learn when a player busts your campaign" is the normal way to learn this stuff in the community.
Sorry for the long-winded answer, because I agree with what you said. The game's shift to high level play is very real, and the wizard does get to shift those low-level spells to more utilitarian spells. And it is a trial by fire, no doubt.