I'm not sure what's happening with that archer guy. It's been made clear at many points in previous chapters that this world has XP sharing. There should be no point in KS-ing for XP. Or is the XP sharing limited to a formal party system that, for some reason, they refuse to use in this specific case ?
Now for the other side of kill stealing… I was thinking in the previous chapter that having official rules that a mob's drop goes to the one who did the last hit is a terrible policy that stifles some classes, even entire roles. It's nice that we're already touching on that issue, I hope the author has a good reason as to why a super big long-established guild would have such bone-headed rules.
Also, cool frogs. This manga really likes them. Ranged poison is always a pain, but I'm not sure if it's worse than that. Remember that Elma was poisoned as a lvl8 back in
chapter 3 and survived with, I believe, zero medical help. As much as we'd like to see him humbled, that archer is probably not in any real danger. (Yet.)