Well, actually, Army did maintain both capabilities for some time, red eye/Rapier and for a while RBS 70/ Rapier, so yes, there has been a capability reduction, and both sides of Govt have been guilty of neglect for decades.Or phrased another way, the army has replaced an aging short range system with a much more capable modern, self propelled system.
It a bit like saying retiring the F/A-18A/B after the F-35 started entering service is a capability reduction.
A Res would be perfect for a shorad system, but RBS 70 is not that system. Its not a particularly useful system these days. Need a fire and forget type system. I work with a guy who did years in 16 AD before it became whatever it is called now. He maintains its nearly impossible to hit a fast mover with RBS 70, it would be handy for helos and drones, but thats about it.