Second addition:
> I think I exhausted most of the available content, but I was still having fun with it and wanted to keep playing.
I bet you didn't! I challenge you to show me a screenshot of your prestige tree. Especially the familiars evolutions branch. How many scorpions did you evolve to named forms? Or turtles? Or eagles? Pets discoverability is the mecahnics exactly for such completionists as you (in a good way), but it's pretty demanding