The personal limit break concept isn't really functionally different than any other gauge mechanic. It works well in PVP, but there's really not a need to have it as a separate system in PVE.

As for the existing party limit break, it does need a rework. I don't know the specifics, but I do know that DPS limit breaks suffer from the DPS value not actually being worth it in some cases. Additionally, as mentioned, some limit breaks never get used. Here are some thoughts of my own on how to address the issue.

Firstly, I'd remove the concept of LB1 and LB2. This helps address the issue of LBs being too weak, not just the potency of DPS limit breaks often not being worth the animations, but also healer LBs which are literally worse than using Medica until you hit LB3. The rate at which LB is gained can be adjusted. Now, every LB just uses 1 bar, and the rate at which LB is charged can be adjusted slightly, though I don't think it needs to be 1/3rd of the speed. DPS dealt with LB3 is not that powerful that it would be game breaking in weaker content. Next, when LB is used, that role cannot use LB again for 5 minutes. So if you use the melee LB for example, you can't use the melee LB again, but you can use the ranged LB, the caster LB, or the Tank or the Healer LB. The further helps support the concept of bringing one of each role, as you could spend all 3 LBs in a savage fight, for example, on 3 DPS LBs.