But for the sake of character diversity, I feel like at the very least a mix of Johns' version and the 90s is in order. If he's just Johns' version then he's just a far less fun older Jon Kent. Mixing the distinctive personality of his 90s style and the more tempered aspects of his 2000s era stuff might be a good way to shift him away from redundancy in the face of Kenan and Jon. A version of his The Just look may be nice (the very bottom of the page). There's enough implication of swag there to let you know "oh this guy used to party" but also let you know that he's not quite as into that as he used to be. Don't go loud on whatever suit he's gonna wear, but make it clear that put just as much thought into the style as he did the substance.
Also maybe give him some slight stubble beard?