I still feel like it's better than MoP and WoD. The problem is that they have very little knobs left to turn nowadays.
They actually have too many knobs, in some ways. Right now they can't seem to dial in the right dps/hps levels. In game design 101 they call it TTK (time-to-kill) which is usually the most fundamental parameter. You usually have a TTK in mind out of the gates based on desired tempo and gameplay mechanics, genre, target gaming audience, etc. In MMORPG theres obviously more variance in TTK between classes/comps, but its generally a starting point for designing arena matchups.
The devs can access more knobs then ever before (separate pvp and pve mechanics), all kinds of gameplay data (more stats collected on each match then ever before), and with fewer talents/abilities left to confound things (pruning). You also have dials with respect to utility in terms of uptime and mobility (ccs, escapes, interrupts) and endurance (mana, resets). If they were smart they might reduce some of the RNG/gimmick proc mechanics, because random chance makes things a lot harder to design for (requires more simulations and testing time).
My biggest issue is that this should have been the golden age (xpack) of tuning and game balancing, and it wasn't. They needed to invite better alpha/beta testers and hire people like Talbadar months ealier. He's a fantastic player with good design/balance knowledge. Instead, the company scum went the marketing route to fix a bad product. They gambled on all kinds of Blizz fanbois and twitch shills (classic twitch headline: LEGION HYPE BOYZ) instead of ironing out these issues before launch, a month in, etc.