Priordials have something much more powerful then lots of health levels, a 1,000 strong mote pool. IE even an E8 Solar will mote tap themselves before the Primordial perfect defense falls
And the primordials are a bunch of E10 monster that explicitly did eat thou the exalted host by the thousands up on the thousands, and that was just the celestial exalted. The amount of celestial exalted that made it thou the entire war without death at least once can be counted on 1 hand. For all the Solar, Lunar, and Sideral combined.
Mate that is exactly the kind of force that breaks exalted, mass mook spam, followed up by some bigger threats is expliclty the best counter to exalted.
The war was slog of exalted continually winding up dead, with only the shards reincarnation keeping things going. Even then thowards the end of the war the Primordials has found ways of crushing the Exalted when they kill them, in such a way it messed up the shard prevent it from finding a new host for a while. Odds are 50/50 if the war had kept going the Exalted would have won or the Primordial's figure out how to capture exalted shards and auto win at that point. The Yozi and the Neverborn both lesser and dumber existences then the Primoridals could figure out how to capture shards so the Primoridals.
Exalted have to be E8 to have a chance of solo fighting a primordial, and even then the Primoridal's vastly bigger Mote pool ensure their victory, so long as they can keep their perfect defense up.
Also it is stated that the charms seen in the books, are mathematically perfect charms developed long after the war ended. The Charms used during the priordial war where weaker, cost more motes, and achieved lesser effects. A fight between a exalted of any type vs their primordial war counter part is a stomp for the second age exalted with their vastly better charms.