Which is true for my observation as well. The question was more in regard to the fact, that I've got sometimes the impression that connection that offer a high first leg rating are preferred and that flight ratings still have some influence beside the overall connection rating. Which doesn't sound very sensible, but better describe some bookings I actually see.
In terms of unrealistic bookings, I've seen passengers flying 90 min to the opposite directions to finally fly back 90 +40 min to the right direction and even pay more for that experience. What I haven't seen so far, but wonder whether it is possible, is passengers flying A-X-A-C.
In AS, flying through the same airport twice isn't possible from what I've seen.
In real life though, I have done LGB-SLC-LAX-JFK rather than just LAX-JFK given it was cheaper and I got a few extra miles so in a way A-B-A-C is possible if you look at LGB and LAX as the same A since they serve the same market.