Truth.
It's not that the fed jungler wins games, is that the other jungler has literally no idea how to jg. What paths to take, when to hold lanes (so much lost exp from pure ignorance), when it's worthwhile to gank, when to counterjungle, when to start dragon, anything. Laning is just last-hitting some minions, mirroring the other guy and not dying. Jungling is so much harder, more dangerous and more intricate.
It's like being first baseman in baseball. If you're mediocre at your best role then you are, at best, a Meals-On-Wheels feedlord jungler. Rito pls.