I think attempting to precisely define Leaders vs Uniques + the discussion about synergy is distracting from the real issue at hand here.
Synergy aside, Leaders used to be significantly more powerful than Uniques in terms of strength and/or capability to affect the overall tide of a battle. Now, Uniques are becoming just as strong as Leaders. Krennic could be released tomorrow with a Unique called Daunting Presence: -20% critical chance, -20% critical damage for all enemies (exact copy of GG's Leader) and nobody would bat an eye, because that's where the power creep in this game is headed.
Granted, maybe that just means that most Leaders are outdated and need reworks. I guess if all the obsolete characters are given the Finn treatment, everything will work out eventually.
