I agree – Retail Shadowmeld killed faction balance, just like Every Man For Himself did after introed in WotLK (dual trinkets was equally game breaking at the time). A superior PvE faction and a superior PvP faction is by definition balanced though.
As far as faction balance, the best move is still to introduce Horde Humans and Alliance Orcs (Defectors). This respects the lore by not tormenting vanilla designs into Tauren Sunwalkers and Dwarven Earthcallers, and a provides a more interesting hat tip to the original Warcraft design of Orcs vs. Humans. If it works, the Defector tag could be introduced for the remaining races but it would need to be tested first (does every battleground devolve into 10 orc shamans versus 10 orc shamans? lol).
There’s a good story there, of a small group of humans who empathize with the horde and rebel against the oppressive Alliance. It opens decent armor appearances for Horde too on a “non-monster” frame. Paladin is available then and human racials aren’t seen as overly onerous.
As far as the orc to Alliance story, there’s an equally good story there of how far someone will go when they’ve been captured and coerced, for example (e.g., “The alliance offers peace! Lasting peace! The horde knows only war!”). It offers Shaman that Alliance loves to complain here about (yet they stay Alliance) and the “best racials” they love to gripe about (even though Hardiness isn’t that great, actually).
There’s a path. There’s also a question though of how to introduce this story and whether or not the tech will allow a human horde and an orc alliance (how to integrate). But I do feel this is substantially better than the damage horde elves and alliance spacegoats did to the lore.