I think one misconception a lot of people have is that the 4% rule is based on the expected return of the stock market over the long term. It isn't. If it was it'd be the 9% rule. Instead 4% is a rough estimate, based on historical data, on how much one can safely spend out of a stock+bond portfolio in the worst times to retire in the last 150 years.
We simply don't have a comparable 150 year dataset of home value and real estate data, and even if we did it would probably represent a sort of broad index of millions of houses across hundreds of cites, not a concentrated bet in a small number of houses in one city, which is what most rental investments necessarily end up being.
It sounds like you're already doing a good job of calculating what you expect for an average/typical return from those properties though: rental rates, maintenance, mortgage paydown, appreciation, inflation, vacancy. But no one can say with the level of evidence we have for the 4% rule in stocks how much or how little you can count on being able to take as income from your rental properties even if you end up picking one of the worst times to retire.