I totally disagree. Have you listened to A Farewell to Kings, Permanent Waves and Hemispheres, not forgetting the fantastic Moving Pictures?
But if they're not prog, what are they then?
Have you listened to:
Karn Evil 9, Tarkus
Close To The Edge, Relayer
Selling England By The Pound, Nursery Cryme
Larks' Tongues In Aspic, Red
That should tell you enough about what's really progressive rock.