Re: Caustic buff/change
I think Caustic also suffers from other issues as well. I bought him first over Mirage, and I've been playing him fairly regularly but as time goes on, his weaknesses become painfully apparent. Most of the other characters are given some kind of mobility increasing or defense oriented passive, ability or ultimate. Caustic, while he does have traps that are fairly useful, their proximity for enemy detection is rather poor and the gas hardly does any damage to be a viable threat to enemies flanking you or even if you decide to use the Nox Grenade ult. His passive is also fairly poor because it "gives you vision" but not even that works 100% of the time and like you said, your teammates cannot even see through it.
Compared to the other legends, Caustic's lack of mobility and the threat of his traps and ult really do * him extensively. I think a proper way to balance him out/ buff him is to give his gas more damage, possibly increase the trigger range of the traps, either change his passive altogether or also give his teammates vision.