Mages definitely are viable, but it’s not a meta set, so I don’t think there’s a current build for it on maxroll. It’s essentially blood nova but instead of iron rose & funerary & rorg you use nailoj evol, volitions, and reilena’s. max our your essence cost and you’ll cast 8 mages per click all with max essence, so that you never have to worry about too little essence to keep them all up.
You can pretty much just blood rush around and pop mages whenever you hit full essence and should clear GR90s in 2 minutes easily - depends on the rift of course, and you may need to optimize your gear a bit to make it work. I don’t have the full build, but I had it working on PTR and it was great.