I would say more 2:1 on some older designs but with newer self checkouts you have walls and additional shelving being added for goods instead of just the normal "end cap" style of traditional lanes. Also, reducing the working space of a checkout lane creates more problems with larger purchases. Have you ever tried to ring up a full cart of groceries with a tiny weight-shelf? Shit's horrific and usually you end up needing to get another cart to start putting items in before yours is empty (if the system even allows you to "remove" items from the bagging area).

Again, I think your process is faster, but the average check-out speed is going to be longer which the company doesn't care about since they're not paying people to check out. If you've never had a problem checking out I think you're in the minority, everyone has had something flagged or "attendant needed" during a check out at this point.