Maybe evergreen was the wrong word choice, but it was their word.
Basically, they made no fundamental, low-level changes to the game, and that's where the issue I have are. High level play. Number of encounters per day needed for class balance. Things like that.
They could. If they across the board halved the number of spell slots, and for some classes daily uses, they would be a lot closer on one of them.
But they didn't. They couldn't and have the "backward compatibility" as describing in the UA (which is more limited than the normal definition of backward compatibility).
Basically, I'm talking about how long before they start fresh and have a new RPG inspired by D&D that they wish to make the new brand lead, like happened from AD&D -> AD&D 2nd -> D&D 3ed -> 4e -> 5e.