One trait could add a slight increase in attack speed to Deadeye making it kind of like greased lightning just not as much (so like 2% or 3%). Or to make it super technical each crit you get while under the effects of deadeye could have a small (maybe 5%-10%, whatever you have to do to balance it and make it cool) to reset your global cooldown entirely.

Anyway, that's my idea I'm sure there's some holes to fill but I hope it's unique. Maybe someday we'll see an engineer like the one in FFT modernized. I personally think it would be awesome.