Yeah, played optimally on a static target most dps jobs will run out of TP in around 4 minutes, that's with using Invigorate aswell. Skill Speed IS a dps increase, despite what a lot of people think, but it's a bigger drain on your resources which becomes apparent in loger fights. It's currently the worst off stat for DRG/MNK/BRD for those reasons and you should probably stay away from it until it maybe gets adjusted.