Summoner is the Job with the biggest problems. It just doesn't feel like a Summoner when most of the player's attention is focused on DoT management, only you only have to pay a little attention to your summon. Your DoTs don't help your pet and your pet mostly doesn't help your DoTs. As such, the pet ends up feeling unimportant, which is a big problem for the main pet DPS Job. It really needs to reverse that, so that the pet is the main thing you worry about and the SMN is mostly acting to support and control it.

As for other Jobs, I kinda wish that MNK was a tank (it was really tough back in FF1-5), that BLMs had more spell variety and support options, and that BRDs had a bigger focus on support. A NIN tank would be cool too, mostly because it works really well as such in Bravely Default.