I never once had a problem from level 1 to 50 with anything you have said. In fact I used to solo some heroic 2+ quests where there was one gold mob and 2 silvers. I play a Guardian though, my brother who plays a Sentinel did have some survivability issues at first but those were resolves after he hit a certain level.
Jedi Knight is a more advanced class in general and takes in general more skill to play and survive without relying on abilities to do so. Also about class quests I soloed most of mine and when I couldn't beat one I would either level up or get help from my brother and reaped the benefits of getting to see both dark and light choices because he was the same class and same level.
I do think some of the Guardian abilities should be Jedi Knight abilities though like combat focus and maybe even freezing force even though at 50 Sentinels thrash my Guardian, though Guardian survivability is under par in pvp at 50, wearing heavy armor but die faster than Sents.
