For all my priest friends who gave up on the holy MT, and refuse to be a smelly disc player, this guide might help you. The first few pulls using this guys strategy I got to 20%, then the 5th pull ended up being the kill. It feels way more “possible” as opposed to juggling Karem, hands, and summoning runes all at once.
good luck friends 
Shadow Priest Mage Tower Guide Shadowlands 9.1.5
edit: sorry friends, seems blizzard patched this cheese strat. Good luck 
ill have to watch it cause man… struggle bus right now and im beating my head against the wall and once i do get to p4/p5, its madness. i either cant burn things down fast enough so i use extra resources… or my kiting is garbage.
The strat in the video feels pretty consistent. The main problem I ran into was just dealing with the hands. You can sometimes get away with not dispersing on the 2nd hand cast if you have enough space between you and Karam to burn it down with Void Torrent. But if you cant burn it down and have to disperse, try to disperse early so the explosion hits just the last second or so of dispersion, because a few times it didn’t come up quick enough for the next phase.
U can deal with the hands mostly by pooling sanity before they spawn. Or in all reality u can do this strat without mind bomb. u really dont need it just run silence. Then when u out range the raest use the right side of where u spawn. the mobs will go there and u still have plenty of time to hit the orbs without worrying if they will be cluttered with mobs on them. U also can rotate disperse and fear to absorb them IF mobs for whatever reason are on them.
despawns for me with this strat…
Thats definitely true, I just found that with mind bomb I didnt have to focus on the small adds nearly as much, which lets me do a little bit more damage to the boss which is what I had been lacking. Without mindbomb I would get a bad rune spawn, then fear would get capped and I would get killed. Im pretty casual and not really the best, so every bit of extra uptime on the boss really helped.
That’s strange, only time I ever had a de-spawn was when I missed a rune and the mob freaked out
That’s why I said u can hit the boss to the right of spawn. As u can still hit orbs and mobs won’t be on top of them. U still have disperse and fear to rotate only if u get rng screwed.
im exhausted and i cant do this… just tried for 3 more hours…
actually mental. got to p5 one single time… and i blew it for no reason. had the long game going…
I didn’t miss anything. I had soaked the rune, and was running out of range for shadow bolt and he despawned. happened more than once. -,-
This is basically the strategy I used for my affliction warlock
You can’t kite Karam long enough to kill Raest so I just killed Karam and stayed far away from Raest until I rotted him down
Also side note: Why is this scaled so much higher for warlocks?
Karam has like 30k ho and Raest has 133k for my priest, but they’re 47k and 200k for my warlock 
Prob because warlocks have that slow curse. Shadow priest can only slow Karam by hitting mind flay only.
Something similar to why Mages hit harder for Hpriest and less for Hpals, because hpriest have a purge.
My heart is pounding just watching it.