Reasons to lock advanced jobs behind anything:

They are advanced.

They do not start at level one.

There is no associated class (so they can't start at 1)

Any story implications or background

Establishing WHY the trainer is wasting their time on you

Mechanics not meant for novices (these classes sound a hair complicated)

...

And we want to unleash this on novice players coupled with a community that is already not tolerant of mistakes?

And you think this will make them stay... By offering a complicated job at an advanced level in a community that runs off vets with its negativity for new players and mistakes?

Simply brilliant.

I work for a Fortune 500 Company and would love to see that kind of executive strategy implemented. Would you like an application?