Reading that hurt my head. lol.To Clarify i retested.
16:9 2560x1440 Full screen display = aspect = full screen image (stretched)
16:9 2560x1440 Fullscreen Display set 1:1 = Full screen image (stretched)
16:9 2560x1440 Fullscreen GPU & Display Set = Blackbars + Input Lag
so no you cannot run Full screen 16:9 without input lag, the only way to run full screen 16:9 as shown above is use GPU scaling creating more inputlag
what should happen is overwatch should do the scaling, which it does not. because 21:9 was an afterthought & broken.
"Fullscreen 16:9 @ 2560x1440 creates black bars"
after retesting this was incorrect. i was writing all this from memory over multiple days of testing