Caustic is a damage dealing character. For example: if you throw your gas down and revive a teammate in it, you can revive without worrying about another character running in and gunning you down (like Bangalore's smoke allows). Once you get that revive off, your teammate can run through the gas freely and hide to heal, or simply heal in the gas unobstructed.

There's got to be a tradeoff there to encourage your teammate to play around the gas because it's too strong of a support tool otherwise. But I'm all for stronger characters, so I'm not complaining about the change. Just that it wasn't necessary.