I think people underestimate Thalyssra. Sure, Jaina has incredible power by average mage standards and she has trained under the best from Dalaran but Thalyssra has studied arcane magic for over 10,000 years and knows what was capable with it before the Sundering. I’m sure she if the Nightborne has a prominent role in the current war, she’d be a significant powerhouse in that regard.
Equally, Sylvanas and Lore’themar have significantly more tactical experience than anyone on the Alliance.
You’ve also got a lot of side characters who could play a part in the fight. Shandris Feathermoon, Hamuul Runetotem, Maiev, Calia, Garona Halforcen.
Lastly, it also depends on where this theoretical fight happens. Malfurion and Hamuul are actually unlikely to fight the other faction outside of their homelands due to both being leaders within the Cenarion Circle and the Circle’s neutral position on the war. This is also true of some other characters and their role.
The Alliance are far more powerful, certainly, but I don’t think it’s as one sided as some make out. My main issue with the whole thing is the story has become human centric, sacrificing the strength of others to make sure that Anduin and Jaina look the most powerful