In Diablo 3, what should be the primary focus of a Lvl 675 paragon with 100+ hours played?
Solution 1:
Yes, this is all this game has to offer. Rifts, adventure mode, Paragon levels, and Primal gear are the "Top Level" things you can do in the game. Once you've done all of that, you've done it all.
The main reason that Primal drops are so rare, and take so long to grind is just so that you have something to do, while you keep playing the game. Other than that, play with friends, start a different character, maybe do a "Hardcore" run.