This is true for the most part, but in the case of Kristin Wiig (and Amy Pohler, Adam Sandler and a handful of others) she was shot into the spotlight in less than a year and remained there. Lorne is always looking for these people who are capable of becoming stars right off the bat. But you're right, most go the way of Jimmy Fallon, Tina Fey and Bill Hader... It takes a few years before the focus is on them. Which is what's obviously happening with Taran Killam, as they keep increasing his screen time because he's a more low-key guy who can do a lot of good impressions and you can put pretty much anywhere, basically the new Jason Sudeikis.