I haven't had any real trouble ranking, including doing classes such as a necromancer or druid. There's usually some people to group with, and if not, stay logged in a bit and usually someone will come along.

Most of the heroes I've done lately have come in around 50-70 hours, I think. Haven't done an invoker in a while, but that would take longer I expect just from mastering spells. Just be efficient in your ranking, and take advantage of quests and down time to do what you can. I had a shifter doing a few ranks killing one mob over and over (boring) while waiting for a group to come.

Alternately, if you see a certain cabal is in power, you could start with a character for that, get help on the way up, and probably reach the pinnacle in time for the power swing.