If something is less likely to occur, I want the mechanics to reflect that
Yes, by setting a high DC

DC setting is an interesting thing if you use 3d6 because it has a much higher impact and a DM needs to be really careful with the DC. Just a few values too high and you rapidly decrease the chance of success. Non-linear rates are much harder to grasp for most DMs.
even if you present it as if that were obviously true.
I repeatedly stated "I don't understand". I thought this marked is clear as an opinion, not as a fact. Let me emphasize - this is not an objective truth. I just would never fit my resolution mechanic to the same probablity curve that is used for standardized metrics like IQ tests or for measuring natural occurences like body height over a population. Its the anti-thesis to storytelling in my eyes. Its used to measure real, natural events. Heroes should be living as outliers of statistics, not forced to be normalized.
I am passionate about this, because its a small subset of the big topic "Statistics ruining art" which I might open up a thread at some point.
edit: I just used anydice to roll 40 times 3d6. Look at this exciting dice log.
output 1: 12, 11, 7, 10, 10, 13, 12, 9, 14, 6, 9, 7, 8, 5, 10, 12, 9, 9, 10, 10, 11, 13, 15, 10, 8, 10, 4, 12, 15, 14, 17, 3, 12, 10, 11, 11, 7, 5, 11, 13