It's a cool idea, but it certainly isn't powerful. You can't even mount the thing as a medium character until 13th level unless you get the undersized mount feat. Plus the drake itself won't even compare to some of the companions you can get from the Beast Rider archetype or the Monstrous Mount feat. The drake powers are kind of cool though and the visual of it is awesome. A small Cavalier with undersize mount can ride it at 5th level, so there's that at least. Make it an air drake and it won't take too long to fly.
I did some number crunching about drake companion vs. animal companion / mount:
Nongood alignment (more options to choose from) > true neutral alignment (?)
15d12 > 16d8
BAB 15 > BAB 12
+9 all saves > +10 Fortitude & Reflex, +5 Will
60 skillpoints > 16 skillpoints
more class skills > less class skills
8 feats > 8 animal feats
+20 natural AC (partially because of size) > +12 natural AC (doesn't include specific companion bonus though)
refuses some equipment (armor, belts etc.) < more openminded
final size Huge (more reach & damage) ~= Small / Medium / Large (more flexible)
+16 Str, -8 Dex < +6 Str & Dex (also doesn't include specific companion bonus)
+4 ability scores increases = also +4
darkvision, low-light vision > animal companion's senses (usually?)
immune to sleep, paralysis, their element > no immunity
vulnerable to opposed element (if applicable) < no vulnerability
6 drake powers, +1 via subtype > link, share spells, (improved) evasion, devotion, multiattack
So overall there is good reason for a drake companion to cost some class features. Up to you whether it's worth it.
Undersized Mount was already mentioned - depending on your campaign, it can be retrained later or not.
I'm curious what the number crunching at lv11 is. The end of PFS. Or where is the tipping point of when the drake is better than an animal companion.
Keep wondering if some form of Summoner might not be a better choice...Not sure what exactly, but seems that using the eiodon would work...