So I did research on rune dragons, at first I thought I could just bring a bunch of sharks and kill these dragons easily, and kill at least 10 in the same trip. But then I realized something, I can't even hit them with melee.

 

Now I haven't finished the quest required to kill them, so I know I have a long way to go before I can even access them. But my question is are rune dragons like boss monsters?

I'd say more like halfway between slayer mobs and bosses. They have some more complicated mechanics but aren't really a boss per se since there are lots of them hanging out in one area.