If you're worried about getting dragons down, and you don't want to put points into Archery or Destruction, you've got three main options.

One:
Get a Follower with ranged attack, to snipe the dragon. Use Unrelenting Force when the dragon hovers in front of your Follower to snipe them, disrupting the blast of dragon breath that's about to follow. Then wade in and start hacking then the dragon lands.

Two:
Don't start the main quest until you're confident you can take on a dragon by waiting for it to land and then attacking it. You'll want a few levels first, obviously!

Three:
Do the main questline and advance it until you've learned Dragonrend. It's a big investment, obviously, but it means you won't have to be scared of the bastards. And honestly, it's the most entertaining, gameplay-wise... playing Skyrim and not killing dragons is like eating a taco with no salsa. There's just this awful feeling that something's missing the entire time.