One of Ceruledge's big stand-out features is Flash Fire. It really has the potentially to cause grief to your typical sun sweepers, especially with terestalization to play with.

The tldr is that Ceruledge will probably be best run as a bulky counter to sun teams: its speed is in a weird place even before boosts, it's boosts are reactive and not pro-active in nature (you rely on your opponent triggering them) and it's not bulky enough to get use out of heals after it starts eating defense drops.

Weak armor isn't bad per se, it's just super niche and largely wastes what's interesting about this Pokémon. Ceruledge has the potential to really prey on a lot of sun sweepers while utilizing that sun boost both offensively and defensively with its signature move.