Anthony,You would be surprised by using some old school methods like simply writing a letter like you mentioned. 

That method will increase your ROE significantly more.Also read the BP book on BRRRR investing.

Would that method work again?

Each method has a cost in both time and money.  

It isn't the metric you can talk about on a national scale, but if you keep buying the same product in the same area it is a very easy quick and dirty method to know how you are doing compared to other buys. 

My interest are house flipping and the BRRRR method.

Additionally, they managed to refinance while the rates were at historical lows (and still somehow cashflow negative ik 😭), so any loan methods that involve changing those rates are not ideal.

I've done various methods and would be happy to connect and knowledge share if you are interested.

Find Brandon's videos on YouTube for the "four square" method of analyzing homes and practice.

Even though I had a full size W/D on site, I still used this method.....