As I’m personally approaching the OL equivalent of higher tier play (level 7 - 10), I was intrigued by this thread. Ultimately, I’ve come to agree @VanGo and @Great_Moustache on most everything that has been discussed so far.
The only thing I’d like to add from personal experience is that it’s a lot easier to approach OL when using a more narrative approach. I tend to focus on how to make things meaningful (read, traumatic and personal) for the players’ characters.
Each campaign “season”, which usually lasts 3-4 sessions of 4 hours each (as we found ourselves having rather busy schedules and rarely get to see each other in person due to geographical distance), has me focusing on one particular character in the group that I want to have some significant impact on or to give some memorable experience to. And the most significant moments for these characters happen at the “finale” of that “season”.
So far it’s worked out for me! I think part of the reason I went this route was 'cause of getting inspired by Critical Role as a show 
By relying more on a personal, narrative angle, each XP point, each level, really feels like they’re growing and improving and learning more of their world. So from that point of view, level 10 is more than enough to have a fulfilling campaign to end on! 