I would not include 10CC, T Rex, Tommy Bolin, Roxy Music, or Santana. Where do you draw the line? Interesting question but if you take any of the agreed upon progressive bands i.e. King Crimson, ELP, Yes, Genesis (with Gabriel) and compare any of the work to "Bang a Gong", "Black Magic Woman", "Love is the Drug", or "The Things We Do For Love", that's where I draw the line.
IMHO