If you're a 6 year old looking to play baseball, do you expect the pitcher to be throwing the ball at nearly 100 MPH? Of course you don't because you haven't stepped up to bat at an MLB game.LOL.
No. I haven't looked at every single sandbox ever made. That's true.
Just every single one that's been brought up as an example in this thread.
Show me a sandbox for D&D where the level of the characters is not built into the sandbox.
It's the same with the adventurers. They could try to take on that high level threat and it will likely be a TPK. So just like I would tell little Timmy that they probably want to try out for the tee ball team designed for their age group instead of the Yankees, I'll make sure there are options that are level appropriate for the characters. They can still go to the MLB tryouts, they just won't get far.
Beyond that I don't see what the issue is.