Basically Starck and Leia will perform almost identically on TM in worst case.
Starck will require his zeta though.
Leia will give 30% TM if she only shoots once for three rounds and lands her 55% buff every time. So some rounds she won't apply buff and some rounds she will attack more than once.
Starck will double buff the entire team every 3 rounds for 20% TM, and at the same time reduce opponents TM by 10% every round (though resistable and requires a full trooper team).
And then you have the added CD from his group buff, +50 Armor Penetration to troopers, decent AOE attack+stagger, assist on Veers' AOE, buffs and TM gain from Veers' unique and synergy with DT, Snow and Shore.
I don't see how adding Leia will make troopers better in any way, unless you have seriously good RNG every single time you use them.
