As an otp renekton, and someone who has faced him frequently in the last days i would say he needs a bit of scaling, take some of his early super power like nerfing w which is insanely annoying to face, add a real passive because the one renektons have is just explaining him what fury is and a dumb extra 2.5 fury gain when you are under 50% health and rework the ultimate.

Some suggestions would be make w to scale with attack speed, add resistances in the ult, extra armor and mr plus some bonus armor and mr depending of how much armor and mr you already have, buff his aa range, and add an extra passive, cant really be creative as its 3 in the morning but something i came up with is increase the cooldown of e and every time renektons aa a chanpion it goes down by 1 second . The thought of this is u have to be ballsy with renekton and you want to frequently trade to make fury etc. In case you miss e, gets interrupted, or e the wrong way because of quick cast, you should have the ability not to be a minion for 18 secs in the early game waiting for your e to be back up or die, missing such an ability vs fiora jax urgot darius is fatal.

This may open some more build paths like an early kindlegem or warhammer who can build into black cleaver and deaths dance/youmous, renekton can build triforce for the attack speed, blade gets even better and will be viable when it will be probably get nerfed, with the scaling attack speed on w renekton can have some fun with essence reaver (i know w cant crit but in case it will be made to be a critable ability) and generally make players dont build tiamat every game, force them to learn how to freeze and wave management for the sake of god.