Debatable. Some players have no problems with dragons at any level besides the first introductory ones.
Dragons are random spawning, for the most part, so level only factors into what strength the dragon is (even then you can still get normal dragons at level 60+). If the game awarded a tougher dragon after a boss then some players wouldn't get many tougher dragons unless beating quests with a 'boss'. Though there are those of whom play one quest after another so then they'd be overrun with tougher 'boss' dragon.
I just think its wierd how i can kick a dragons butt, then i get my butt handed to me by a frost troll......
That svcks.