I'm still levelling my lock through RoK (76 now) but have run 3 other toons to 80. I honestly can't imagine trying to level up from combat xp in T8. There are so few linked encounters and combat xp gain is just terrible. The solo quest lines are by far your best bet to level up. KP, then Fens, then Jungle, then JW. You'd miss a ton of AA by not doing them as well. I know they can get dull but it will be much faster and more productive in the long run (some of them have decent gear loot) to just hang in and run the quests.