I thought it was just the heavyweights that have regressed

Have to agree. Less spectacular fighters all round, less strength in depth across the divisions. And nobody fights each other which hinders progress.

Heavyweights now are better than ever. It's nostalgia for old fighters in all weight divisions that makes many overrate them.

It's called nostalgia. Ali used to get floored by cruisers and it happened multiple times. That doesn't happen in this era, cruisers can barely even move up let alone become champions. Foreman has one of the WORST defenses of all time, I mean Wilder is LIGHT YEARS ahead of him in defensive skill. LL got cold clocked by Rahman & stopped by McCall. Etc. Pacquiao is a legend and has had his body preserved through modern technology, nutrition etc. We've seen multiple 40 year olds in fantastic shape, back in the day dudes used to get all fat and out of shape like Foreman in his comeback. Being old these days is nowhere near the same thing as it used to be.

The skill on average has declined but there are still stand out fighters: Loma Canelo Fury Crawford