Because Saturday Night Live producer Lorne Michaels has actively avoided the kinds of major cast shake-ups that the show weathered in the ’80s and ’90s, it’s become harder to define recent eras of the show. The Aykroyd/Belushi/Radner/Murray era is easy; 1975 until 1980. The Carvey/Hartman/Myers era is easy; 1986 until 1995. But Kenan Thompson has been on SNL for 19 seasons. Kate McKinnon was on for a solid decade. More than ever, large chunks of the ensemble don’t disappear; instead, casts bleed into one another. When McKinnon started on the show, Kristen Wiig was still there. At the same time, some of her other early cast members will still be around next fall when the show returns for Season 48. Well, maybe. The departure of McKinnon, Aidy Bryant, Pete Davidson, and Kyle Mooney does feel...