you are literally just saying, monarch is only a universe buster when he unleashes his full power.
His full power is inside his armour, he himself can open the armour at anytime as he opened the armour slightly to blast superman prime which hurt him. And this is the dude who tanked a galaxy buster at a weaker state.
This shows that without even unleashing his full power, monarch already has enough energy output that surpasses galaxy busting attack potency.
So armour breach or not dsnt change the fact that monarch can wipe out all of asgard with a gesture
As prime is immune to magic and odin dsnt have a prayer going hand to hand with prime.
Man Prime is stronger, faster and more durable than odin, and also strikes better.
Between monarch, superman prime and superboy prime, the only person odin has a chance against is superboy prime. Monarch and manprime are far above odin's paygrade. As one can destroy the universe and one can tank it