I’m working on something similar, also PRM on hardcore with a Warlock. I selected Occultist because you apply RR at range, but it’s also challenging because it also lends itself to a build with very few keybinds and that makes for a tricky devo path. Mage Hunter is for sure more tanky, but I like the simplicity of Warlock. Just maintain BoD, use PRM and CoF. Super easy.
The issue with Sage + Seru path is that it badly lacks OA. But I very much see the value in using Sage alone with a green path.
This is @mad_lee’s take on a PRM Mage Hunter: [1.1.7.2] Expelliarmus! 5:20m Crucible 150-170, SR 75-76 facetank PRM Mage Hunter[c+][sr+][vid]
My untested Warlock variant is also in that thread: https://www.grimtools.com/calc/bVAdMnl2 as well as a Sorcerer from @djnat : https://www.grimtools.com/calc/a2dMP95V