Got all the first 4 scuttles, was 5/1/0, and still 2 levels down to the enemy's 4/2/0 top laner

I understand that junglers needed XP nerfs to prevent the level 3 free gank, but solo laners honestly also need XP nerfs to stop them from snowballing out of control on levels.

Enemy Jax (with TP) solo kills my Rengar (with Ignite) at level 1. When Rengar gets back to lane Jax is already level 3. Yet I play it great, I took both scuttles on the first clear and got a kill mid. Meanwhile Jax got another solo kill on Rengar.

Then I ganked Jax when he was up level 4 to 2 on Rengar and got a kill there. Then got a kill on their mid and jungle then Jax again while taking the next 2 scuttles and counter jungling the enemy krugs (and obviously Jax got 2 more solo kills on Rengar in that timeframe to be 4/2).

I literally never did nothing. I was always farming camps/scuttles or doing ganks and ALWAYS getting a kill for every gank.

Yet the enemy Jax top is level 8, and I'm level 6 - even though I have 1 more kill and 1 fewer death.

This is an age old issue. There's nothing in this game that can match the level lead that a solo laner can get against a bad lane opponent, other than the other solo lane. If enemy top gets extremely fed, then your mid needs to be right in line with him or else it's GG. Jungle and bot can get twice as many kills and they'll still be behind in XP, and that early XP lead just makes it impossible to do anything against them...

Yes, junglers needed XP nerfs. Honestly though, every champion needs XP nerfs when ahead. You shouldn't get a big chunk of XP for killing someone 1v1 when you've got a 2 level lead on them... Make people carry with item advantages, not innate stats from a level lead...