TSM isn't always there to provide a bonus to melee damage. Sometimes its there to take advantage of alleviate some of the downsides of a high-heat curve, like loss of movement. Or atleast that's sort of what seems to be the case sometimes.
The Project Phoenix Raijins and Grand Crusader IIs are such designs it seems. I'm not really sure its effective, but they don't come across as "Okay, I'm designed to ride this heat curve so I can beat up another mech." Rather they come across as "I expect to overheat, and so this might help a little bit."
The Ebony is in a similar boat. With its Stealth Armor and ERLL, you don't want it getting in close to melee, but with its weaponry, you want the TSM to kick in and negate any movement mods that might come u from a screw up on your heat curve, or if you get hit by heat-producing weaponry.
