Basically, the changes made in the last patch make the activation too unpredictable, since we have two separate cooldowns and one of those can have different durations. We have traits that pair up weapons (flamethrower and elixir guns) and then we’re penalized for using both of them with unpredictable behaviours.
I’ve been playing with an engineer for a long time. I still haven’t understood why you did change that trait. Having multiple kits is already penalizing as it is, since they aren’t too great by themself, use up utility slots and you can’t put traits for all of them anyway.