Not all of those daily quests were from Lich King. I had dozen or so PvP daily quests from outlands completed before getting that achievement. Still I did do a lot of them. Each morning I run through the multibox friendly ones that are available to me. But they only net 20100 xp per turn in. Lets say all 50 were from Lich King thats only 1,005,000 xp. Thats 2/3 of one level in the 70-80 range. Also if someone went to Lich King at 68. Thoes last two levels to 70 would have required much less xp as it was reduced in a previous patch. So yes, the daily quests help, but did not put me 5 levels ahead.

With going to lich king at 68 and no dailies or instance runs. I would conceed at most one maybe two levels, not 5. There is no way I can see that I completed 7+ million more xp doing the same content.