there was a lot of great alt comedy in the 90s with stuff like The State and Mr. Show. I'd argue that shows like that really paved the way for Tim & Eric (in fact, T&E got their big break thanks to Bob Odenkirk who produced Tom Goes to the Mayor)
Tim & Eric definitely brought that type of comedy more into the mainstream until it was no longer "alt" anymore. because yeah, at the time Dane Cook and Carlos Mencia were the biggest names in comedy