Inverted perspective: Strong Armor could make a powerful impact, but the armor itself is compromised by doing so, either through damage to itself or simply not being worn properly after the strike. At the same time, Armor is heavy and Cumbersome, and given Armarouge's design, might be energy based, meaning it could also "shut down" after firing a big shot. This one is mostly a flavor discussion because I assume this move is mostly used for hit and run Tactics, so the Defense drops probably won't impact much if running this Pokemon.
As for Ceruledge consider what his biggest threat would be if he's a fast Glass Cannon type of attacker: Passive damage, since he's going to either want to KO his target without being struck or get the hell out if he can't. Ghost/Fire w/ Flash Fire is a pretty cool type for a Physical attacker (Fighting and Fire Immunity, a decent few Resists like Ice/Grass/Fairy, no Burns), but even assuming he never gets hit directly by a major attack, there's still concerns of being stalled/walled by Weather, defensive pivoting, Entry Hazards, recovering targets, Contact Damage/Punishment, etc. Healing off that scratch damage would do wonders for longevity on a Pokemon like that, and Fire is a more spammable type than Fighting or Bug, for example.
This is also considering that its main STAB is probably going to want to be a Ghost Type move for better neutral coverage, so you'd be using the hypothetical ~75 BP STAB on a specific set of targets anyway. Would have to make defensive teams wary about their answers or switches, because if Gen 8 is any indication, several Pokemon like Weavile, Melmetal, or U-Turn Pivots have to REALLY watch out for chip damage taking them out against their intended targets, with the inverse being true that a Life-Drain Sac at a bad time could undo a lot of progress on a potential Offensive thorn.
And this is all assuming Ceruledge is indeed too frail to meaningfully take neutral or resisted hits, despite having a prominent if less extreme amount of armor in its design. It could end up being akin to Hitmonlee and Hitmonchan, where one of those two is ostensibly the defensive one, but the reality is moreso both being attackers and one just having MORE Attack. Ceruledge could still be reasonable for neutral damage and just not be made to outright tank opponents the way Armarouge is meant to. The similarly built (but unarmored) Gallade actually had decent Special Defense, so I feel reasonable assuming that visible armor is supposed to suggest some amount of defensive prowess.
