Stupid First Time Theory
What if all the killers and survivors are different iterations of themselves, that's how there can be multiple of the same survivor in one trial and multiple different "back stories" for the killers whenever a new skin is released. The vanilla killers are the first basic iterations that the entity scooped up, but the entity is a multi dimension hopping villain meaning it could easily get multiple killers at different points in their own timelines like scarecrow billy, or ww2 nurse (those 2 don't seem the dress up type so to have them dressed in costumes "just cause" seems a bit strange). They're the same people having gone through different things, like experimentations for the hallowed blight characters or costume changes like for ghost face or legion. Plus it would make sense that the entity would want more than just 4 human souls at a time seeing as how large -for lack of a better term- the entity is, so why not have multiple trials going on at the same time. That could also be a lore reason for ranks, the entity has a set of killers that are "lower level" (killers at the beginning of their killing careers) so that "lower level" survivors (survivors who have recently been taken by the entity) can have more hope of escaping and going home. Putting the top tier trapper against a bunch of new survivors means people dying quicker, which leads to less gens being done which means that "hope" would dwindle fast meaing less sustanance for the entity. Same thing could be said for perks; Different killers and survivors experiencing different things throughout their lives leads to them having different skills when the entity takes them. Plus the idea that the entity or even Vigo or someone constantly resupplying the survivors with different outfits like pizza boy outfits and bright pink hair has no advantage to either side.
I know that multiverse theories are dense now a days but it makes sense to me. Again this is my first time looking into/trying to understand the lore as i am a casual gamer of dead but i thought it'd be an interesting idea and thought I'd share. Thoughts/Criticism?