I can't really imagine this system pissing anyone off. You can catch up reasonably fast but the more hardcore players that play throughout the entire expansion will still be ahead by a fair bit. Currently the person with the highest level is at 37, most people are probably not even at 30 yet. And a lot of people stop caring after certain points because there are minimal benefits to keep grinding AP. 2 crit, haste and mastery for every level is negligible at best when it takes a week to get a level.