well, that's a great review ! and the album is indeed worth his Classic status !
overall, I agree with your review but two tiny small details made me tick :
1- Deep Purple's keyboard sound maybe very influencial and they're probably the most successfull band using it. but then, Hammon B3 organ was heavily used in many prog/hard rock/psych bands starting from around 1967 (get informations here :
http://www.gepr.net/geprfram.htm then use searchtool for Hammond)
2- Gillan is an excellent singer, no doubt about it, though the first to make this kind of vocals famous is Robert Plant... Sorry but Gillan took it after when Ritchie's wise brain decided he needed his Robert Plant !
apart from that, I agree 100%.. they indeed gave birth to Prog Metal (while doing it simpler and melodically in much more pleasant way imo) and that's the one bad thing I would have to credit them with.. :evil: