“Some historian” is a bad citation.

I’m very good friends with a medievalist professor. Something they said to me recently was interesting. Today, most medievalists don’t really like the term “feudalism” and instead see serfdom as an extension of Roman slave systems. Not chattel slavery, but definitely not a mutually agreed upon and beneficial economic relationship. I’m not so sure that “serfs didn’t actually work all that much” is aligned with current consensus.