The metal/armor is relatively useless if they can disable it the same way the Lancelot was back in season 1.
The contrast between your ideas and mine is that you're thinking the Suzaku way, "I'll fuck everything with superior tech and firepower" where as I'm thinking more conventional, Schniezel/Lelouche-ish way where one responds to a hueg armored artillery unit with a counter-attack of smaller, faster units.
From what I gather reading about the Mordred's specs, the armor is thick enough to impair mobility and close-combat, it is as you say, the Mordred has a wide array burst of missile launchers, and the armor alone can withstand most Black Knight melee weapons, however it is for the most part, incapable of outmaneuvering the Flight-pack Akatsukis.
Your "wide range discharge" is in effect, a suicide self-destruct bomb, that or will leave the Mordred powerless(there is always a drawback after all). Also, why would you want to be in that situation anyway? It's a desperation tactic that could have easily been avoided had the Mordred been issued with better maneuverability.
As it stands I still bet on it being able to disengage the bulk of armor. It ought to be overhauled a bit though. As it is it looks like it can't function without the Avalon nearby to provide assistance. Doesn't seem very becoming of a Knight of Rounds to need a babysitter.