So is the fun over now that I've hit 51?

[BiG SiP]

i quit my alt cleric at 51, and this was even with end of life red XP Boost (circa 2014?)
highest chars Were 58 via live and red
not sure i can do it with out quad kiting
will be amazed if i can ding 50 on green

It becomes unfun? seeing the glacial XP progress, for me it always ends up the same:
Am i having fun or wasting my life thoughts, this kills the game for me