I have trained students for their PPL with vision in only one eye and I have flown with a Capt in a large Transport category aircraft that had the same.
Apart from the obvious you couldn’t tell the difference in skill level.
As far as the student who pranged the C172....i say it somewhat jokingly as I only have my own experience and anecdotal snippets from others: 3 out of a 100 are gifted natural pilots. Combination of spatial and mechanical intuition and spades of common sense.
They’re the lucky ones and when encountered should be encouraged to pursue a career in aviation.
On the flip side of that coin we the 3% that cannot be taught how to be a safe and proficient skilled pilot. They lack the correct combination of before mentioned traits.
They vary from 250 hr PPL’s to the quadruple failure of every exam to the never solo which are obviously the most extreme cases.
I’ve personally flown with an individual who would return after a 6-9 month hiatus and 100-150 hrs missing out of his logbooks.
Every instructor we had (5-6?)tried and tried and tried again and eventually we ran out of instructors and that’s when he left.
We thought he had in excess of 250-300 hrs dual instruction with no solo.
The other 94%? They have to work hard at achieving their goals in aviation like I did.