First of all, there might be reasons why "they should just..." isn't as easy as we may think. And second: I don't see it as a problem. Maybe because I levelled for a long time without heirlooms. Raising first 9, then 10, now 11 characters (15 if I count the one I deleted in lv between 40 and 70) is sth I have done in the last 8 years and at the end of each x-pack my roster was pretty much filled with max lv toons.
So it boils down to perception if there really is a "heirloom" problem. Seeing how fast my monk outlevels zones...that 30% more or less wouldn't be the be-all-end-all.