Oofta
Legend
I have kinda more had the opposite issue in that 5e is designed to go 1-20 and fairly fast, and (unlike 3e IME) plays smoothly 1 to 20. But then you are at 20 and there is not a lot of support; I am running an E20 game with the DMG Epic Boons system and it works well, but is not as satisfying as levelling up I think. And monsters - well how many times can I reskin a Kraken?
Also, as others have said, 5-10 remains the sweet spot in terms of the traditional adventuring experience. So I am thinking if maybe I should be looking more to an old school BX-style ethos of playing 1-10 as the adventurer levels and looking at 11-14 as 'Endgame', for politics, war and territory development. In contrast to 5e's RAW XP system this will require much slower advancement after 10th, and discouraging the notion that PCs will reach 20th.
I'm also wondering about the possibility of E10 play and having PCs stay in the 'hero not superhero' zone indefinitely. Maybe for a grittier campaign.
I did epic in 4E and after a while the story just got weird. For me you can only ratchet up the threat level so far before you're no longer playing a standard D&D campaign. Sure for a while you're fighting demons and what not but what's next?