I haven't tested yet, as I'm not one who's bothered by the current difficulty of Overland, but I would like to point something out. The whole "people on lower settings come and make battles trivial" thing already happens, just in the opposite direction. Someone battling a WB might be testing a new build or just having fun and Mister McFiveHundredThousandDPS comes along and absolutely nukes it in two seconds.
WBs aren't meant to be claimed by any one person to beat, honestly no Overland content is (aside from instanced stuff clearly). Usually though, you can find WBs that aren't being camped or anything (especially these days when Tome Challenges have people going between a few specific WBs, haven't tested the rerolls on the PTS to see of there are a wider range of Bosses for U50 yet), and even on Live it's rare that I'm doing stuff and see people jumping into random fights with trash packs, so I doubt there's going to be much worry about your fights being interrupted a whole lot by people on lower settings. Most of us staying on Adventurer aren't going to bother going after mobs unless they're near something we want/need to collect
And Public Dungeons and Delves also aren't typically super busy unless it's Witches Fest or people are doing a "complete Group Event in X/Y Public Dungeon" Challenge, or it's a place where Leads drop. So I would say it's likely the same thing, in that you won't be running across too many people that are 'stealing' kills.
Also someone mentioned mobs still having basic attacks. I don't think it's realistic for every kind of mob in Overland to get entirely new mechanics added, but maybe it could be coded that the higher the difficulty setting, the more often and faster mobs attack and use things like Snares, Knockbacks, and Roots? That way you have to be paying more attention, react faster, and be smart about your resources.
