It's good in the sense that people won't feel left behind if they miss a patch or two, because they can catch up when the new ilvl tier is out.
It's the other way : players coming back after a break have to go through a catch-up phase before doing any new content because of vertical progression.
With horizontal progression, it's possible to start with new content immediately after coming back.
Which doesn't forbid new awesome skills and gears.
And it doesn't forbid some verticality either, just less steep.