What you just described is arena, except with harbingers thrown in as well. And you don’t seem to like arena.
That is because you’re not a programmer. These things take time. GGG has their processes very streamlined at this point and yet they only add one mechanic every season, not 5 or 6.
Not only that, but what you consider great endgame content, lots of people will hate. That’s just part of human nature.
After all, plenty of people like arena, even though plenty also hate it. Same goes for PoE’s delve, or PoE2’s trial of suckmyass Sekhemas.
This is likely why they didn’t want a detailed roadmap, because some players would then start to say that it’s wrong and should be something else.
It probably doesn’t concern you that much, given your endgame activity. It does concern a lot of players, especially the altoholics (to whom the game is supposed to cater in the first place).
There are a bunch of devs that also play the game. They even created a room on the discord server for the devs to stream playing it regularly.
New and casual players will very rarely, if ever, reach level 100. It’s one of the reasons why they don’t want to add a paragon-like system post-100. They don’t want players to feel obligated to reach level 100.
In any game there will always come a point where you finish it. There is no more after. In LE it just comes sooner than in PoE, because PoE has had more than a decade of adding endgame stuff.
But PoE also has a “I’m done with the game, now what comes after?”.
That is why in all these games you get lots of players at season launch and they all fall down to below 10% of their peak later on. Only a few players keep playing past a month.
And those aren’t usually the grinders or min-maxxers. Those are the casuals that like the game and keep improving things.
The grinders and min-maxxers are done with the content in less than a month and move on to the next game on the list. They “finished it”. The only thing that changes is how long it takes them to do that. Which is usually around 2-3 weeks for PoE, 2-3 days for D4 and 3-5 days for LE.