This is exactly why there should always be a "fail state". So they're "godlike heroes" that can resist a 20 mph crosswind while standing on a 3/8 in diameter rope? My suspension of disbelief only goes so far. Even in DnD based novels, they didn't have this godlike ability, including one in the Dragonlance series that actually was a God.
I don't know if my acrobatics bonus was +15 or not, but I survived being blown out of the back of a pickup at 45 miles per hour, with only some road rash to show for it, thanks to my martial arts training. It's amazing the things people can do in real life, when they've trained for it. But I don't see them walking that tightrope in a 20 mph crosswind.
If you think a check should be extremely difficult, then just set the DC to higher. Your "walking across a tightrope in a 20 mph crosswind" would much more appropriately be a DC ~25 Acrobatics Check ("Very Hard"). Given that the maximum skill bonus in D&D 5e is ~20 (+6 Stat, +12 expertise, +2 magic items), even this PC would still fail such a check 20% of the time, including on a 1. Almost all PCs would fail a higher percent of the time. No need for 1 to be an auto-failure.
Edit: Similarly, then your DC to remain mostly unhurt in that situation was less than [21 plus your bonuses], allowing success on without a 20 being an auto-pass. A spread of 1-20 on the d20 is HUGE considering that most checks range from 10 (easy) to 25 (very hard). This d20 randomness helps to represent the few amazingly unlikely achievements, whether that's lucky or unlucky.
