I rarely play as Caustic to really comment on the gas radius or damage (as I never pay attention) BUT I do play with a Caustic teammate. What I will say is that sometimes I find the gas has a negative affect on team play and gunfights.
First and most obvious is team mates gas has the slowdown impact on you. I get why that is in but then it can just become a frag fest or a wait (for both teams) until the gas clears. I don't think the effect on team mates should be removed altogether, due to balancing, but surely there is another way.
Secondly gunfights where both teams have Caustic. I hope I'm not alone in this but in this scenario i feel like it's just 1 on 1 with the other 4 wondering what's going on. There's no way to differentiate between enemy and team mates gas so unless you're feeling brave or have a teammate with on point communication it's a spectator sport. Again, surely there is another way. Can gas not become another colour in this scenario or maybe have the slowdown affect (but not the damage) on the opposing Caustic when in friendly gas?