You need a bit of both to force enough 2+ saves and 4+ MW saves to wear him down.
Currently the only thing capable of throwing out high-volume attacks in our roster is Knights, Warriors and Skinks.
Knights are generally MSU due to groups of 10 / 15 being difficult to get into combat, and 5 Knights is nowhere near enough to even dent him.
Warriors look a bit more appealing. I think a good charge roll would make it pretty easy to get a full unit of 20 Warriors with spears into attacking range. With All-out Attack, Hand of Glory and Serpent Venom, the math suggests we take less than half of his wounds on average - which isn't great.
As for Skinks, let's assume a fairly unrealistic optimal scenario in which we have 30 Skinks with Boltspitters and Clubs buffed by the Skink Priest's CA, Hand of Glory and Serpent Staff, who shoot Archie and then charge to get 20/30 into combat. Let's then buff them with the Steg Chief's CA for a veritable Skink blender.
Even then, we're only taking 12-13 wounds off of him. This would have been great in 2nd Ed. but the prevalence of healing mechanics makes this a little less impressive.
Bringing him down reliably would require the input of basically our entire army. The Everchosen is a seriously impressive Dark-Souls-tier boss fight. In many cases we might be better off focusing down his support and playing the objective - which won't always work; he's very difficult to ignore as he's fast and can hit like a train. But not much point in trying to chip him down unless you're going second and feel like gambling it all on abusing a double turn, or, the rare opportunity presents itself where you can dog-pile him with everything you have (likely multiple Skink unit / Salamander volleys + melee) and hope for the best.
In summary:
