Guild Wars 2

I found out recently that the trait deadly mixture (additional 15% dmg for elixir gun and flamethrower) isn’t effective with flamethrower, in fact, using flamethrower decreases the damage (I’ve compared it in game). I tried for elixir gun and it’s working fine. Am I missing something or it is bugged?

well my concern is, is there a way to try builds (mostly traits) besides in spvp?

My reason is I want to try my builds to my friend or anyone at anytime.
Why not in spvp? Cuz it has ranking or more like competitive win rate score (the reason why I haven’t tried one).
and both in WvW or spvp, everyone is hungry for kill, so neither one can be a good place to try for builds.
I’m still new to this game, if anyone might know if there is a way or it has been there already, pls tell me