Tell that to the writers. Magical Mystery Cure anyone?
That kind of proves my point. The cutie marks there were artificial, and therefore were unrelated to the capabilities and personalities of the ponies. The swapped ponies were all failing badly at their new lives, and were only trying that because of the spell altering their minds. The point of the episode was that following a destiny that was forced upon you is wrong.
The other episode with artificial cutie marks, Cutie Pox
did have Apple Bloom get the talents with them, but she didn’t actually get an interest in any of those things. Rather, she was compelled to perform her new talent. Compare that to natural cutie marks, where they only reflect abilities and interests that existed beforehand, and don’t force them to do anything.
We’ve seen the mane six get jobs unrelated to their cutie marks/talents/whatever. They all got a job on Cherry Jubilee’s farm without a problem. There are lots of ponies that don’t seem to have clearly defined cutie marks or talents that directly relate to a job, and they still find work. Plenty of ponies have changed jobs.
I don’t know where the idea that ponies can only get jobs because of a picture on their butt came from, but it isn’t supported by the show.
They only get a given cutie mark because it reflects their interests and personality. They want to take jobs that they like. They take jobs that are related to their cutie marks because their cutie marks are emblematic of what they are interested in.
The ponies decide what form their cutie mark takes. It is a reflection of them. A natural cutie mark exerts no control over them because it is only a symbol of what is already inside them.
Incidentally, I’ve always thought that Cutie Mark Failure Insanity Syndrome was supposed
to be a joke. It’s basically the most complicated way to explain something, especially since known cutie marks/talents are rarely directly related to the cause of a breakdown. I’ve never seen any even vaguely compelling reason to think that it’s a reflection of pony psychology.