Thermal is a great set for certain team compositions. The trend of building for def means people neglect resists, so often the thermal shields actually add survivability rather than just excess over the cap def. Thermal is a jack of all trades with heals and both offensive and defensive buffs and debuffs.
On corrs I like to pair it with ice, but on a def I could see a number of blast sets having synergy. Electric for end drain, sonic for -res, etc.
Good thermals keep several teammates forged and pay attention to positioning to get maximum endurance recovery for the team with heat loss. The self heal opens up options for patron/epic pools. I generally try to get 165+ global recharge and switch between musculature and cardiac alphas, usually musc.
Ovrrall, thermal is overshadowed by cold, nature and even elec for hard mode damage mitigation/healing, but the margin is well within the range of skill distribution in that the best thermals are far better than average colds.