I don't regard Deep Purple as a 'Heavy Metal' band at all.
I do think that the Mk II Deep Purple line-up (Lord , Blackmore , Paice , Gillan & Glover) was one of the finest Rock Bands, irrespective of genre.
To my ears - 'In Rock' and 'Machine Head' remain first class studio 'rock' albums - and 'Made In Japan' is the definitive live 'rock' album.