In fact, experience can be a liability, which is why in modern times sitting legislators running for president never beat an opponent who isn’t also a sitting legislator: as a senator or representative you can’t both do your job, which is 90% horsetrading, and avoid supporting bills that will come back to haunt you.
I agree that PB has an unusually good chance, which is why it will be interesting to see what happens with the Iowa shakeout. However, there are so many candidates in this race that he and his people have to see this first as an investment in the future.