So my two last characters to get level 90 is my rogue and dk....Right now, my rogue is 87. He's pretty geared out. Engineer helm, epic legs, rest blues. I'v tried all 3 specs, with assassination being the best imo. But even if I say " the best" I was only pulling 25-30k with CD.
Question now is. On my frost dk 86, I'm pulling 40-45k with green/blues. Nowhere as geared.
Are rogues just that? Or does it get better at level 90? when you start to start a certain stat?
Rogues just feel far behind until you've started getting epics. Once you're mid-T14, you should be fine, and ahead of the pack in early/mid-T15. This isn't really an agility-wide issue, but it's an issue for rogues compared to other classes.
Assassination should be ahead for pretty much all gear levels (excepting major weapon level discrepancies) short of ~525+ gear. If you're mini-AoEing while leveling, or need help single-target, combat's cooldowns and blade flurry are very impressive.
I leveled a rogue in cata, and back then I didn't have crimson tempest and fan of knives we got at lvl 81 or something so aoe was a nightmare while leveling. Besides, mobs dies more fastly so for a class that has their combo points on the target that can be frustrating.
My dk i could spam obliterate with killing machine and howling blast + D&D on aoe and do really high damage. I don't think classes are balanced at all at that level.
Even at level 90 I think my frost dk does better damage in lfr than my combat rogue even though i have timers and everything and think I'm ding it right. but I'm only like 470
I'd say it's pretty much about the scaling of gear. I've stated in many occasions that MoP rogue leveling was by far the worst leveling experience so far. You're squishy and die a lot cause you can't handle the incoming damage and can't pull out decent numbers. Around 30-35k through levels 87-89 was pretty standard for me, mostly as played in normal instance blues or lvl 85 epics that where still far superior to MoP greens. All I can say that it gets better at 90. Not necessarily straight away in heroics, but t14. Tier 14 is still mid performance but solo play is improved. Cutting edge T14 and now start T15 is where we get ahead. Topping meters even as combat in a single target fight is now possible. 90-140k, is a big stretcher but definately nice numbers depending on fight. Solo survivability is still the same, take time you get hurt, but bigger numbers help with shortening the time you have to take. The leveling experience compared to paladin, shaman or the dk you mentioned is just not worth mentioning. Shaman specially was very enjoyable to level. Paladin and Dk don't have to worry about pulling several mobs at all.