$1M house is NOT cashflow friendly
1) Any vacancy from a big house is going to directly eat away your cash flow. However, if you split $1M into 3 houses, one vacant house will have less impact due to diversification.
2) Rent efficiency is NOT high for high priced house. A $1M house can yield about the same rent as a $70W house. Rental rate is NOT linearly proportional to the price of the property.