Rengar is not OP because of his numbers or gameplay. He is OP because of nerfed trinkets and wards.

Back in season 5, Rengar was never a problem. He had his strength: deleting lone squishies out of thin air. He also had his weakness: teamfighting. Why was teamfighting a weakness? Because against an enemy Rengar, the ADC can buy a pink ward totem while the support and jungler (positioned further out) can buy a sweeping lens and detect Rengar from far away at crucial times in the fight. Mid and top can either take their own sweepers or get upgraded yellow trinkets to deep ward and warn against Rengars coming in from the flanks.

Currently, the support has to spend an entire slot and very limited gold income on pinks late game while the ADC can't do anything. Solo laners can no longer ward as effectively due to no green wards and weak yellow trinket. Red trinket also does NOTHING against a Rengar since not only is the radius tiny and you don't actually see him, his red outline is delayed, meaning it's way harder to hit skillshots on him than usual.

This is why Rengar had a HUGE jump in win rate in preseason.

My suggestion for nerfing Rengar: don't. Revert the nerf to red trinket and make pink ward trinket buyable again, even for a huge cost like 400 gold.

This literally only affects Rengar and a Teemo who stands still. It doesn't even affect Twitch or Eve since Twitch is either backline or far-away flanking while Eve is visible when she is in range anyhow. It also affects Shaco a bit, but not anywhere near as much as Rengar. Rengar will also not be UP because of this change since he was at a healthy 49-50% win rate throughout season 5.