Nooooooooooooooooooo!
Sooo Warhammer online? And that turned out so well... Nope.
Not really equivalent at all.
In Warhammer, each race had its own classes. But every race had a tank, rDPS, mDPS, support class. So essentially factions were just mirrors of each other with different favors.
The OPs suggestion is that the Horde have to 1 healer while the Alliance has 4 healers
So you basically want Warhammer Online? No thanks.
Due to balancing, the classes would end up being mirrors of each other on both factions: having the same functions and numbers with different visuals. It ends up feeling very shallow and lame.
For example, the engineer class in Warhammer had stationary gun turrets. The chaos version of the class was a summoner with a demon pet that was permanently rooted in place. Why? It had to match the engineer perfectly and their turrets couldn't move, so the demon on the other faction couldn't either. Really dumb design.
Does fit neither the class fantsay nor would this leave the game in a good state. Are you fucking shitting me? 1 healer for the horde? GTFO.
Actually, this class/faction setup may work if some serious changes are made to the game mechanics.
Horde DK can be made a full-time healer in blood spec (it's logical - blood means life). Tanking spec then would be Frost or Unholy, which fantasy lore suites best. I think of Unholy, for it's classic WC3 AOE ability Death and Decay is parallel to Paladin's Consecration.
Shamans have to be buffed to be on par with Priests. But it's 2 against 4 healing specs still, so the Horde DPS classes can be given much more effective self-healing abilities. This even have some lore meaning. The Horde is about to be self-sustained, about freedom and so on. Alliance on the opposite is about mutual aid and support.
This is all but pure speculations of cause.
Would be pretty bad, but I'd love to see faction-specific classes, such as Warden for the Alliance and Dark Ranger for the Horde. These would be two new mail classes.
The problem with that is that most classes actually come from the alliance if we base this on the WC3 model, everything you put in alliance is right but you need to add DH cuz that's illidan, a night elf, and DK, arthas, a human.
So it's either not balanced or makes no sense with any kind of lore logic.
With DH's being bound to the Faction Elves, I loved the idea of exploring Race based classes. Possibly something that could fit in with your base idea in that each Faction/Race would have its' own identity via the playstyle.
For Example, what if Gnomes and Goblins, given their vertical/physical limitations, had Tank specs based on their technological prowess?
A gnome can't physically absorb the same impact as a sturdy Dwarf, but an energy shield that absorbs incoming kinetic force can! Maybe a modified Arclight Spanner in the other hand to help dispense of all that built-up energy and keep the aggro up?
A goblin can't match the strength of an Orc, unless he hops in his modified shredder before going in to battle. Smaller but sturdier, with all manner of gadgets built in to help stave off, annoy and set fire to combatants.
Just an idea I like to think of every now and then, nothing I expect to be put in WoW... But I find imagining up Race based classes kind of fun
As others have said, this wouldn't make any sense at all.
The majority of all DK's are, canonically, humans.
The majority of all DH's are, canonically, Night Elves.
You can pretty much go through and figure this is almost universally the case for every class, largely because the Alliance is written better as a "power player".