Reptile doesn't have strong armor or fast normals, but everything else about him heavily offsets these problems. Where he doesn't have good armor, he has one of the fastest specials in the game, which, combined with the slow travel speed on his projectiles, he is capable of starting his offense, or simply falling back to bait countermeasures to his offense. And his only armor move helps set up his offense as well, so it's not completely dead of a move.
MIT, about Skarlet, iaCD is a good countermeasure to Reptile's normals, especially d4, but Reptile can spit her if he feels one is coming, which gives him a spot to either forceball, or EX forceball to bait out the armor.
Also, with Reptile's low hitbox and d4, his defense vs a number of characters definitely jumps farther than you'd think. Having armor isn't always going to save you, and you're going to have to learn how to defend the hard way instead of falling back on it with whoever you play (because it will always come with a fee to use armor), so extra things like those defensive tools help.