The funny thing is, the juggernaut build that most take on him, isn't even the oppressive build.
There's a super high armor penetration build that a small group of Renekton players run, it's full damage high armor penetration, ending in like 61 Flat armor pen at full build, it also has Black Cleaver so you get the percent shred paired with Renekton's E, so proper fury management you can one shot just about anyone. You actually start out with so much armor penetration you practically deal true damage to anyone who isn't a tank, and tanks feel like squishies to Renekton's standard build.
The only reason he's super strong is because he has faux tankiness while possessing a lot of damage. If the game weren't as fast paced and snowbally as it is, Renekton wouldn't be that big of a threat, he'd be in the same position as seasons before where he ends up falling off at a certain point and he's just a mid level damage tank.
I think the change on Fervor has solved a lot of the Renekton problem for this patch, he's still very strong obviously though. The only adjustment that you could make to him would be to hit his base damages perhaps. I personally don't want any changes as he's one of my favorite champions and I like his power where it is, however I can understand the need for some changes since he is one of the few top lane champions that is naturally capable of turning a gank into a double kill for himself.
You'd have to make very gentle adjustments otherwise you risk dropping him straight into the trashcan immediately, but personally you need a meta shift to do this properly rather than actually nerfing him, that way he can hold a place, even if not a good one, if the meta then shifted out of his favor. He hasn't received any actual buff since 5.9, it's entirely the way that the masteries, items, summoner spells, and meta have changed that have carved out his current position.
damn well if you use his E to dodge tentacles.