Exaggerated though it may be, I think this is one thing that a lot of people never fully understood, myself included.
You climb a tree at level 1 - it's DC 10. It's a level 1 challenge.
You climb that same tree at level 30, it's still DC 10. Because it hasn't stopped being a level 1 challenge.
It was actually 13th Age's explanation that let me fully understand, DC math is based on the approximate level of the obstacle or terrain, not the players. Yes, most terrain or obstacles that a party faces will likely be around their level, but they don't need to be, if it doesn't make sense.
Anyways, it doesn't really change your point at all. Just felt like commenting.