This is getting into weird semantics so I am guessing some of my group’s games would not be alien to you. But then again who knows?
If you don’t even consider levels and challenges—-ever—-plunking a low level character in a super high level module will have consequences.
If you consider level of party and challenges, you are putting your finger on the scales and it’s probably in the favor of characters. If not, I have not tried that experiment.
While I get what you're saying, it isn't always so cut-and-dried.
Sometimes a (let's say mid-level) party might inquire as to what adventuring possibilities exist in the region and get three or four answers, maybe something like:
"A while ago some villagers up north asked for help in finding some vanished people, a group of adventurers who went up in response have now disappeared as well"
"Strange lights have recently been reported around Belekka Ruins" (the ruins are a well-known landmark some days west of town)
"There's a skull-shaped castle on the north coast that's always had a well-earned foul reputation, someone ought to go in and clear it out"
"It's springtime, which inevitably means Orcs are raiding out of the Andalusian Hills again"
Now I-as-DM know what's behind each of these and which one is vaguely suited for what level of party, but the players/PCs don't; and if they just pick one and go without making any inquiries (or even paying attention to the minor clues contained in those write-ups!) they could soon find themselves wading through something trivially easy, or stuck in something way above their pay grade, or dealing with something more or less suited to them.
But if they make some inquiries and-or pay attention they could quickly realize that raiding Orcs might be something best left for lower-level adventurers to deal with, the skull-shaped castle has its reputation because over many years nobody - includng some pretty powerful people - has been able to clear it out (in other words, it's way above the PCs' pay grade), the missing adventurers were a slightly smaller and lower-level crew than the PC party, and nobody knows anything about the lights at Belekka other than they first appeared about three weeks ago.
End result: they still have a viable choice as to whether to investigate goings-on at Belekka or try to find the missing people-plus-party (or to go elsewhere and do something completely different; or to try and do both in sequence); and I'll have an adventure in hand for each option in full knowledge some of them might not see play.