Which means people who play 12 hours a day will have an advantage, no?
Only in quantity of drops and, of course, the extra stats and gear flexibility. Of course, there will still be players that find the most uber-rare items with like 1 hour of lvl 70 gameplay while the nolifers grind away in frustration, so there's that aspect of it too.
I was simply pointing out that exp isn't everything (or even anything), but I will say that removing the campaign kinda ruins the "magic" of "starting over", instead just making sure everyone goes into repetitive grind mode (like the ridiculous CotA runs that people did pre-RoS launch).