Yep it's a pain to go and find your way to the join domain options these days. It certainly shows you the way Microsoft is thinking about these things. Domains with GPOs were a really sweet way to manage everything but MS have realised they can nickel and dime you to replicate the same functionality on a subscription model with Azure ADDS, so bend over boys.

All MS's stuff feels half finished these days. I believe they call it 'high feature velocity'.