Maybe I'm just old school (or maybe I'm just old... ha!!) but I never really thought of Kansas as a 'prog' band...
And this is coming from someone who saw Pink Floyd on their Atom Heart Mother tour, back in the Fall of 1970 (in a 3,000 seat auditorium) complete with 25 piece orchestra and 50 voice choir!!
Here are a couple of my faves from the 70's:
Peter Hammill probably has one of the most intense voices I've ever heard...
...and Annie Haslam has one of the most beautiful!!!
(all of the key members in these bands have kept recording and performing through the years,
although VDGG is down to a 3-piece now...)