In all honesty, the TP decay is kind-of annoying, especially for Lancer. The ability Invigorate is the issue. TP decay is -300TP every 2 seconds. Invigorate increases TP by 100 every 2 seconds, 150 with Version 2. This means that the only use for the ability is at the beginning of combat, but battles are over before there is any real gain in TP. I would be far more in favor of TP only decaying in passive mode.