That article is on point. You don't
just make money from cash flow.
It - correctly - points out that the 50% rule isn't the only way you make money. It's not the be all, end all for ROI.
It also - correctly - doesn't dispute the 50% rule. It IS the best method for creating a pro forma cash flow / ROI.
My monthly PITI + property management are at about 50% too. That's why the concept of chalking up the other half to expenses makes me nervous.
It may make you nervous, but if you don't plan for that, you'll take it in the shorts later when you aren't prepared for vacancy, repairs, capital expenditures, etc.
Taxes and insurance are already included in the 50% rule. So you wouldn't subtract PITI and chalk up the other half, you'd just subtract P&I. Basically start with your gross rent. Take 50% away for all expenses. That's your cash flow if you own it outright. If you have a mortgage, subtract P&I, and that's your cash flow with mortgage.
Most months you will cash flow a lot more than that. But some months you'll have to replace a water heater. Or your unit will sit empty for a bit. Those months your cash flow will be quite a bit less, perhaps even negative.
For example, I have rentals that rent for 1.1k. P&I ~ 270 (PITI ~ 400). Most months I keep the spread, or 830. But long term I'll actually keep about 280/mo (1100/2 = 550 to expenses. Minus 270 P&I = 280), because the months with more expenses will bring down that average (for example months where my cash flow is -2,500, which I have had .. tenant moves out, I get new paint/carpet, no income that month, pay the mortgage of 400, etc.)