In that case the "DM decides if it is appropriate to hide" is completely redundant with the base gameplay loop. Might as well preface other rules with "The DM decides if it is appropriate to attack" or "The DM decides if it is appropriate to cast a spell".
He also pays people to play video games for him using his account, and then brags about his "achievements". Scummy doesn't even begin to describe it.
How you do one thing in life is how you do everything...
Game designers are more like artists than business people. Unless management has them on a tight leash they're more likely to follow their own creative vision and then look for commercial arguments to support it than the other way around.
Most people in D&D can't do this though. A powerful spellcaster can tell you that he spoke with the gods, but you personally have no way of verifying the truth of such statements, you have to take them on faith.
As a miniatures enthusiast I prefer dragons to have more or less the same appearance aside from color, that way I can paint any dragon figure as any color dragon and it will fit.
Only content that's been superseeded by new versions is considered legacy on D&D beyond, so most of the 2014 stuff outside the PHB isn't legacy.
If you want to play with 2024 content only you'll have to restrict available sources to the 2024 PHB.