One thing to consider is which version are we playing on? A player who started, say, in 2017 and is Challenger now probably has no idea what S2 league was like in terms of minion damage, jungle routes, time to kill objectives, or even some of the champ kits.
Additionally there is something to be said in terms of teamwork and prep time. So the rando Challengers have time to gel as a team or just a random show match on a whim?
If it's taking TPA or something vs a team of modern challenger players on a patch none of them played on that much where the challenger players had a week to practice, then it wouldn't be close IMO the challengers would win. Even without practice I think it's close but still the challengers.