Frost mage here too, and yeah - dragons are the wall every pure frost build hits eventually. You're not missing a perk, you're running into a hard counter.
The issue is twofold: dragons have naturally high frost resistance (especially reds and elder dragons), and they're flying. Impact staggers them for like half a second if you're lucky, then they're airborne again and your spells can't touch them. Augmented Frost and Stability help your damage, but they don't solve the fundamental problem that frost just doesn't work on these enemies.
You've got a few real options without abandoning frost entirely:
One, grab some shock or fire spells as a secondary. You don't need to spec into them - just carry a novice-level destruction spell for dragons and use it as your "oh crap" button. Sounds boring but it genuinely works. Shock in particular has good range and interrupt potential.
Two, get your hands on a decent staff - staffs bypass your spell resistance to some degree and let you save magicka for more important stuff. There's that one you get from the college questline (won't spoil it) that's solid for frost mages.
Three, if you're on PC, there are mods that rebalance destruction to be less hardcountered by specific resistances, but that's a bigger load order conversation and you're running pretty vanilla right now.
Honestly though? On Adept, a secondary fire or shock spell is like 30 seconds of playtime and solves the problem. Dragons are supposed to be rough for pure frost. It's not a build flaw, it's just how the game's designed.
