Dunno about that. I lived through the 60’s and nobody back then considered The Who as heavy metal. Turning the amps up does not heavy metal make.
I think there are metal elements in Live at Leeds, and had their next album had the same heavy, frantic, molten edge to it The Who could have been a bigger seller than they were. However, Who’s Next was a relatively tame effort (though it is a strong album despite clunkers like Behind Blue Eyes and The Song is Over) and by the time Quadrophenia came out they’d passed on the metal genre. They’re still the best band ever.