Is Conflux a broken castle?

by the way, he doesn't cast Armageddon on himself, at least not on everyone, and even with the Sphere, their fire immunity doesn't disappear!

Really? Try it yourself, and then tell me... :)
Vulnerability Medal + Armageddon = Instant loss :) No unit retains its immunity in this case... We're not talking about the Armageddon's Blade, but about the Armageddon spell.