Yeah I agree.
I love M+ as Arcane but you hit the nail on the head, how awesome would it be if we had something like DB in our rotation (to say nothing of cauterize)? Supernova is a joke and you have to talent for it. Meanwhile Fire gets DB baseline on top of everything else their kit already offers. The whole thing is just disgustingly unfair and I am just too fed up to deal with it anymore, not when it’s this blatant. Maybe I am getting too old for this, lol.
I’ve been focusing on my Shadow Priest for now. My main alt has always been a Destruction Warlock but they managed to screw that spec over too. I have a Boomkin but he’s Zandalari for the dino forms and I can’t main a Horde character coz eww. 
I really hope they get their stuff together with the balancing but right now even 9.1 doesn’t look like it will deliver. Right now, it’s looking like a skip expansion for me. They really should have called it quits after Legion, imho, it’s been nothing but downhill since.
I mean the lack of reliable CC procs and the inability to store them IS the crippling mobility issue. It just depends on how you look at it I guess. But also, not to harp on how much better Fire has it compared to Arcane, but Searing Touch anyone!?? Not only is it an extremely powerful execute but it offers virtually unrestricted mobility during the most crucial moments of a fight when all the boss mechanics begin to dangerously overlap. In the meantime Arcane can do nothing but fire off an ABarr (at a considerable ramp up loss I might add) whilst desperately trying to dodge things and stay alive. Arcane just can’t compete with that and neither can Frost tbh. Bottom line, it’s yet another expansion where it’s Fire or go home. At least in BfA it didn’t get this out of hand until the very end with the corruption shenanigans.
Yes, and mobility is Fire’s niche. Balancing Arcane shouldn’t be giving the same mobility as Fire. Leaning into the Arcane class design is to buff its damage and burst potential to counteract it being less mobile.
Idk if doubling down on strengths while ignoring weak spots is the best way to go.