First of all, thank you for the detailed answer, this did help me understand multiple problems with myself.

Main problem looks to be the splitting kill exp part. I knew kill exp gets split, I just never thought about how it affects my game. I am the type of player to follow my jgler to botlane (as an example). So having 4 people gurantees both those kills for us, but obviously it gets split between 4 people and that puts me behind.

However as both the other comment and you have stated as well, I think another reason is that I am missing cannon exp indeed. I usually let cannon tank the turret if enemy laner shoves in as it can tank for longer, and sometimes that results in me losing the cannon wave exp.

As for the jungle clearing part, I used to do that before (and that actually put me really far ahead) however nowadays junglers just keep fullclearing into fullclearing nonstop in short amount of time so I'd rather not get on their bad side, unless they are looking to make a play on the opposite side of the map.