It’s kinda interesting to watch how much heavier metal has gotten over the years, honestly.
For example, Helloween. They went from something like Keeper of the Seven Keys back in the late 1980s, to, off their most recent album in 2012, Paint A New World and Kill It. Huuuuge change. From…
I imagine it’s something akin to a Heavy Metal Arms Race. Every band is like “You think that band is Metal? Check out how Metal THIS is!” and it just escalates. Also, better production technology and sound quality allow for a heavier sound without it becoming a garbled mess. Imagine modern metal on a vinyl record.