Here's the thing, the time consumed will be less if you're killing a mob 2-3 shots rather than lets say 6 shots so faster leveling for heirloom people. Also, heirlooms are still giving exp bonus so you'll get more exp than without heirlooms. I have no idea about increasing lvl cap, since I don't think they made this change yet but I'm certain that this happened because a month ago some dev made a video about this and how they wanted to "enhance" the leveling experience.
Idk if I am missing something but wherever the fuck it says that the heirloom experience has been removed?