Marking is only necessary in low DPS groups where focus firing is the only way to get things killed (provided you don't lose patience and quit due to how long it's taking), or if you're just starting out and want to minimise your damage received. I used to mark all the time, but it's pointless in higher level content, which is where your character will eventually spend most of his time. The name of the game is chain pulling, and once you get good at that, everything else will feel too slow.

Incidentally, Paladins only have problems tanking brayflox normal and Quarn normal. They can easily handle Sastasha through Haukke, and Stone Vigil and up is a joke.