I think the difference is that when Metallica started to finally make videos, which was the Black album basically, those singles that were marketed were not as fast as prior diehard fans liked

Albeit, slower drumbeats are in Seek & Destroy, For Whom the Bell Tolls, and many of the more popular tracks during the heralded era...

I just don't see a big evolutionary difference that many cite

I think Metallica suddenly became this larger popular thing that fans felt they had to share and before it was this non-MTV/counter culture thing that fans could feel like was their own