Obviously Rome and Greece both had slaves and class systems, but I'm wondering if any philosophers of the time were bothered enough by the inequality to discuss it, be it in a socratic dialogue or some lost work of philosophy. I imagine Marcus Aurelius discussed the role of the Emporer in his writings, but is there anything beyond that?
As you are waiting for an answer I can link to some earlier ones. Some philosophers discussed these issues, but they tended to not be overly radical since they were generally of the groups that benefited most from inequality. There were always a few exceptions, of course.
u/toldinstone and u/Iphikrates discuss the opinions of elites (including philosophers) on democracy here. Philosophical opinions on slavery have been described by u/Spencer_A_McDaniel (here), u/Llyngeir (here) and u/mythoplokos (here). Finally our good old Iphikrates has also discussed Marcus Aurelius specifically in this answer. More can be said about this, of course