I'm no expert so i'm the wrong person to ask. I suspect its probably a bit more complicated than your conclusions. But it does fundamentally make sense that its a more difficult indication, maybe next to nothing will work.
I certainly doubt lly will spend another penny in RRMS is how I would look at it. They're in this for an awful lot of money already and it's probably a relatively trivial amount for lly to get to the finish line on spms.