Jump potions wether you agree with them or not are being implemented primarily to allow new players a way to catch up to the new expansion or thier friends level if they choose to pay for it.

The Dev team has decided for whatever reason that the two new classes will start at 50 and they will have experience thier own reasoning behind it.

Simply put its a level playing field for the new jobs, jump potions enable catch up, what you're asking for is a paid method to jump ahead of those not willing or wanting to pay, which is not the purpose of the potions.

Either grind out the 10 levels or start the expansion as a job you already have at 60, it won't get changed at this point and it shouldn't.

You'd have been better off just petitioning that the jobs start at 60, though it still wouldn't change anything at this stage.