Yeah, I'm not completely getting this. The article reads as if the study was done just to waste time and really they wanted to propose their "if rideshare is done sustainably" suggestions.
I live in a place where a car is basically required for normal life. As such, my experience with ride-share services is exclusively when I'm traveling and thus don't know the area super well. Ride-share rides "replace" a transit ride, yes, but in that it's theoretically possible to have taken a different option, but does that mean that the public transit option is good or reasonable at that time or place?
Like, if my party and I have been out drinking for a while and are leaving, could we theoretically walk to a nearby subway station and figure out a couple of changes and get back home? Probably. Is it a lot easier to go "Hey Lyft/Uber please pick us up and drive us home while I wobble drunkenly in the back seat"? Yes. Does this count as a "replaced" ride? If ride-share didn't exist, I would have had to take the public transit option (which is assuming that normal taxi's didn't also exist). If I knew I wouldn't be able to ride-share home though, is there a serious chance that I would have just not done what I wanted and instead done something else while staying sober so that I could public transit home? Yes, definitely.
Ride-share to me just opens a new list of possibilities. If I know I'm relying on ride-share and I'm not worried about the cost, the list of things I can do goes up. It gives me more options for my evening. Are we saying here that that's a problem and that people should feel limited to what they can access via public transit? I mean, fair argument but I don't agree with it.