What if "Draconequus", is just another name for the Eastern Dragon? Spike's flame has sparkles even when he doesn't use it to send letters that doesn't show up around any other dragon's flame. He also isn't affected by StarSwirl's spell, a reality-warping spell. As well, Spike isn't affected by Discord's mind spell. And while Discord might have thought he wasn't worth it, Discord also mind fucked Big Mac, an even more minor character, so that wouldn't make sense. Spike might be immune to memory or mind control.
Maybe he's immune to Fluttershy's Stare like a certain lord of chaos...
Now, I'm not saying Spike would be able to warp reality to his whim like Discord can. I believe that Discord gets his power from his insanity, not from his race, as well as the reason he is so taxidermied. Spike would not. Spike would however, be able to use magic (like pyrokinesis, teleportation of self or objects via flame and possible mental magic like illusions). I feel like he would mostly specialize in Alteration and due to his use of a quill, Runes and Sigils. I think Alteration and mental magic due to his connection to the color green, with seems to be associated with Dark Alteration and Mind Magic like the Sirens hate-inducing song, Sombra's mind-controlled soldiers eye glow, and, of course, Chrysilis's mind control.
Wow, with Spike eating a dark magic book, losing his mind to greed, and being connected to the one of the Dark colors, is he going to end up being a bit dark? Well, he did burn at least one person to death before hitting puberty...
Also, I found this on Wikipedia, so take this with a grain of salt but... Further sources give variant lists of the nine animal resemblances. Sinologist Henri Doré lists these characteristics of an authentic dragon: "The antlers of a deer. The head of a crocodile. A demon's eyes. The neck of a snake. A tortoise's viscera. A hawk's claws. The palms of a tiger. A cow's ears. Sound familiar?