i dont have a problem with poison can be countered by healer aura.
but leonzai.. i can feel you bro.. i too have a gunslinger just like you, and the only good think she has is her aura, which is poison when crit. while her skill is nowhere as good as other archer. and this poison too seems like underpowered. the aura skill say every other hero in aura will poison opponent. but in fact poison not stack, so only 1 poison maxed can be applied even 3 hero standing in aura. not to mention poison only triggered if crit, and to get crit is not that easy even with my hera gunslinger sometimes my mystic seems to crit more lol. And while poison or dot normal to be conter by heal over time, but poison should counter big defense. but in fact poison seems damage according to opponent defense or mag or if not still have its damage cut by mechanic if attack mid or rear line. this should not happen in my oppinion.
seems it is just my false to going gunslinger, hope can get something different or unique by going poison way, but it seems should just go 'meta' forever. seems it just normal for any game to have underpowered class and it is us or my false to pick that class.