"Couldn't care less" is pretty much an impossible statement. The subject of what you don't care about has to be on your mind in order for you to respond to it. So you have to care one way or the other in order to utter anything about a subject.
Everyone knows that "could care less" implies that you may be aware of a subject but really don't think about it to give an opinion one way or another.
The OP stated that Rupp will not medal and then followed that up with two detailed explanations for that opinion.
That takes a pretty high level of "caring" to not only start the thread about Rupp but bring in a lot of information on the subject.
All of the people that could actually care less about Rupp than the OP haven't even considered anything about Rupp's 2020 season.
Care less is almost always a careless phrase to use.
A good way to use it would be if a person brings up a subject - "What do you think about Galen Rupp in 2020?"
And if you hadn't given it much thought you could say "I could care less about Galen Rupp in 2020".
But the person who asked that question could not honestly respond, "Yeah, me too."