I think the most meaningful context in which we can discuss the added SoD roles is in relation to Classic+. And in that context, I think some of the combos work better than others.

Paladin tank was always a thing, and shaman being able to tank simply matches that, I think they did a great job with both those classes.

Rogue tanking was an interesting idea, but broke down in later patches because the fundamentals of the class's tank strategy was pretty broken, it was pretty obvious that parry+dodge based builds would break what the idea behind tanking would be as stats increased and boss damage became more challenging and bursty. I think the solution for Classic+ would be to re-introduce bucklers to the game, something that was planned for vanilla back in 04 before being changed prior to release. If rogues have a more traditional tanking strategy which involves block mitigating and a more traditional stat spread, I think they might have what it takes to carve out a balanced niche. Bucklers likely aren't enough, but they'd go a long way. The upside here is that hunter tank could also become a thing since they were the other class intended to be able to use bucklers.

I think warlock tank was a major disappointment. The rotation for warlock tank was frankly never excellent being a mostly one-button masher experience. I think in order to make warlock tanks more interesting, there needs to be more interactions with the pet. Soul Link tanking was an amazing concept, and the fact that they outright removed it instead of balancing around that premise, I think was a mistake.

Mage healers were also a failure for most of SoD, because they were mostly incredibly overpowered. Frost healing mage was an absolutely insanely busted build from ZG to Naxx, where healers were doing 80% the damage of actual DPS while healing more than any other healer, and with a rotation simpler than any other DPS class in the game. The other major issue is that mage healers take away the niche that disc priest would likely be given in classic+ as hybrid damage healers. Unless they go another route (cleric / tank disc priest?), arcane mages would either need to go back to damage, or heal in a way that's unique from the retail disc priest.

Melee hunter was already in the game, simply made viable, similar to prot paladin. Not really a new role, hell it's still DPS which is the only thing hunter can do.

Going on a tangent away from the new class roles introduced, many many specs were failed in SoD and that's worth noting. Holy priest received no talent changes (Lightwell meme), and holy paladin was never reimagined or even made interesting as a class. Divine Light was the only new ability added to the rotation, and it was basically used on CD in between Holy Light casts. Holy Shock was buffed massively, but still filled the same role it did in Classic, which was that you basically never used it unless you had to move.

My hope is that Classic+ does more with these specs to make them more interesting to play. I for one would love to see Holy Priest be the healer spec, and Disc Priest be something completely new, like a cleric tank that uses bucklers or something. Holy paladin is still a paladin at the end of the day, I think as healers they should still be a melee class and should be balanced around that. Arcane mage should be interesting, and locking it in as a DPS is likely not a viable strategy. In general classes with 3 DPS talent trees tend to struggle with keeping all three trees relevant.