(particularly true for single family homes)  Tom and Aaron may have different experiences.  

It does beat the expected inflation rate of 2% set by the Fed.Rents will remain about the sameWhat’s interesting is they also expect:A 11.7% increase in existing home inventory followed by Single-family new home starts growing at an impressive 13.8%. 

On average we have spent about $60k to reset the clock on a 1960's single family home.

Also, rather than taking a large amount of money and investing into one single directly owned property, I can split it up into much smaller chunks across many different passive investments.

Own 10 rentals in Columbus Ohio and building another 21 new build single family houses in Florida that will be a clean BRRRR that will be free and clear.

Do you think a duplex is generally a better investment than a single-family home for rental purposes?

Only luxury single family houses will be built. 

Quote from @Edward James smith: Hello, I currently own a single family house with an ADU, and a duplex.

Instead of debates and personal opinion, look for proof https://www.ladbs.org/docs/default-source/forms/plan-check-2017/single-family-dwelling-duplex-plan-review-list.pdf under G (Interior Env) which defines the minimum requirement of a habitable room (aka bedroom or bathroom).

I also have a joint venture with them on a single family property in Philadelphia that is currently rented.