I'm climbing by abusing the fact that my jungle opponent is usually secondary role or auto-filled

This role really should not have reached this point. It's become so undesirable and frustrating to play that nobody wants to queue for it, and now we're left with this scenario, where I'm farming off role or auto-filled jungles for LP, which just perpetuates nobody wanting to play it.

The primary issues are that the burden of knowledge is too high and a single early mistake can make the game unplayable. If you ask yourself 'do I win a fight with the other jungler right now' at any point in the game and don't have a 100% correct answer, but your opponent does, you're likely going to lose.

This is almost entirely how I'm winning games with Udyr; the only champions I can't fight early are Karthus and Kindred, and they're rarely picked by people who don't main them. More often than not, my opponent doesn't know that they can't fight me and I kill them before level 4, and then I use that advantage to run around their jungle for the rest of the game. They have to concede all of their gold and EXP to me, or if they try to fight me, they die and feed me more gold. There's really nothing they can do after that first early death.

At the same time, if I get matched against someone else who mains jungle, the match is a clusterfuck where one of us wins or loses based on our team mates' picks and lane performance, which is just as frustrating.

There really needs to be a solid plan for fixing all of these issues in the pre-season. The current EXP changes will do nothing to mitigate any of these problems.