The Fletcher comparison is bugging me too.
For one thing, Fletcher was much the brighter prospect when he was a youth team player. At one point, SAF was considering giving him his first-team debut when he was still only 16 years old. Gibson was never this much of a prodigy, not even close.
Unfortunately, Fletcher's development stalled slightly when he picked up some serious injuries then took a while to cope with the physical nature of senior football, due to his slender frame.
Gibson, on the other hand, is already a big, strong young man. He has a massive physical advantage to Fletcher when he was the same age as Gibson is now. This means he can't be expected to improve simply by filling out as he matures(something which you could always see would improve Fletcher massively as a footballer) It's other aspects of his game which need the most work and there's no guarantee they will improve as much as Fletcher's athleticism did over the last 2 or 3 years. Fletcher has apparently recently put on 12kg of muscle but Gibson can't improve his awareness or movement as easily as eating more tuna and lifting a few weights.
I still think it's harsh to write Gibson off completely but it's daft to assume that his development trajectory will match Fletcher's. They're completely different footballers.