Having just finished rewatching Loki (dear goodness it's such a phenomenal show!) and recently rewatching Quantumania, I have to say I'm satisfied with the Kang storyline ending here.
Now, I wouldn't have minded more of the Kang story. However, Loki managed to end things on a very high note AND in a way where Kang has already pretty much been taken care of. Even Scott's unease at the end of Quantumania about something worse coming can be chalked up to Kang somehow having played a role in stopping Doom, and now Kang being defeated means that won't happen (I doubt Marvel will actually explicitly address that dangling plot thread from Quantumania but they could if they wanted to).
So basically, I have no issue with the "Big Villain" role being handed off at this point.
(Speaking of Quantumania... any chance the Kang variant Mobius mentions at the very end of the series as causing "a little ruckus on a 616 adjacent realm, but they handled it, so..." is referring to the events in 616's quantum realm?? I tried but couldn't clearly read the file B-15 was holding 😅 )