is summoner after awakening good solo?

As the topic says or are there any class that does the job better?
From what I read it ain't possible to solo any class after level 89, is this true?

With a boxed buffer and if you know where to go it's good solo. Would not play one solo without a Nostromo, though.

Mages and Summoners can solo easily after 89, not sure where you heard that from.

Issue is not really soloability, but XP rate. Soloing at 9x in fields is like soloing level 79 a few years ago (pre-GoD). It simply isn't a viable path unless you have Birthday pots or always have a 100% XP Rune on you (maybe 50% would work, though).