when leveling at 71 requires millions of exp... just a few thousand at level 29 doesnt really seem that different. sure, it makes training a bit easier, but hey... you can skip training for 4-6 levels at a time with five guys.
also, they eventually catch up. dont ask me how it happens, but it does.
lastly, dont waste your grant levels on your leveling toons. if it bugs you that much, have all the lower levels pick up an extra quest. pick up a quest to be sent somewhere and send them there. easy. or while you're leveling, give one a collection quest while the others skip the collection quest.