Yes!!!
I'm glad you mentioned the secret room and alternate ending - was worried nobody was going to find those for a while haha.
So there are two final bosses, and the second one triggers based on whether you "learned the lessons" (E.G. how many lore objects you interacted with). It's easier if you find Room 9 but you can pull it off either way if you're super thorough.
I had a lot of fun with the mage build, too. Did you use the crowd control spells at all?
Thanks again for giving it another run and sharing your perspective.