There's no way you could have actually watched him and came away unimpressed. What games did you watch?
Here is a PFF piece on him before the start of his Junior season:
https://www.profootballfocus.com/news/college-nick-bosa-is-the-best-defensive-lineman-in-the-country
I watched every single snap that Nick Bosa played in his college career. I never thought that he had any chance of being as dominant a player as Joey Bosa during his time at OSU. Before his freshman season, I probably would have agreed that he was overhyped because of his last name.
While I still think that Joey was a slightly better player because of how good he was against the run, I wouldn't have a problem with someone thinking Nick was an overall better player. Nick was definitely the more dominant pass rusher and jumped off the screen in a more obvious way.