Dumbing down is the negative alias of accessibility.
It's the glass is half empty vs the glass is half full.
Apparently gamers are selfish. More non selfish proposal would be a good skill adoptive game.
problem is, that no easy task and add to complexity of game production. So often limited to a setting like Easy Normal and Hard etc.
Large funding's and production cost needs large target audiences.
I have no problem with it. Dumbing down is fine with me. Most singleplayer games are some how story driven. So I like a smooth story flow. Instead a QTE that rewind as a A-B loop. replay the same part n times. Or a end boss you try to beat 20 times. That conflicting with story flow.
Also games have a difficulty that is perceived not constant level trough the game levels and gamers differ in how hard or easy a situation is solved.
So a game that dynamical act on player skill and adopt in a smart manner would be great.
Some games have more then 4 difficulty levels.