I think the answer is that it really all depends on if your role changes from one job to the next.

If you're a Gladiator, when you make the switch to Paladin, your playstyle doesn't change because you're still a tank. You did tank stuff as a Gladiator and you're doing tank stuff as a Paladin, except now you've got new toys to play with. If you're an Arcanist, now you have the choice between staying a damage dealer (in which case, just like with the Gladiator, you don't really do anything different besides have new toys to play with) or you can switch to healer (so you're doing something brand new and different than what you had been doing).

In other words, if your role doesn't change, 5 job abilities may not feel like enough because you're generally still doing the same thing. If your role DOES change, then they start to feel good, because those five abilities have to be enough to make you perform your new job good enough to be competitive.