The problem you just explain with one person outpacing the other and having to play alone is solved by level sync. It keeps the base of the game the same but lets friends and groups play at the same level and do the same activities with the only barrier being what the lowest level person can do. Besides that you pointed out the one major downside with a sync system which is having to take away abilities…but this game doesn’t have that issue since we get everything right away pretty much (can’t say i loved that to begin with, part of leveling’s biggest rewards was always attaining new skills/spells). You scale down the level and gear stats of all the players to the synced players level and if done right they should be playing pretty much like if everyone was at that level.
If your going to scale everything for every level…why bother with levels? Its now become only a gear gap which could potentially be skip by quickly or be made to feel useless since it will have a minimal effect until endgame.
I have yet to see scaling not pretty much turn out that way even by major MMOs with giant budgets and teams. It just encourages going as fast as you can to endgame where things might actually matter again.