Second post to the same topic to add clarity.
You are correct in that the way all of these comparison calculations work are all incredibly similar, but it seems like you're not super clear on when to use these different rates and their interaction with each other. Here's a little more info that should help clarify the differences.
- Risk Free Rate: when you compare your deal against Rf, this is the risk-free-rate-adjusted return of the deal. Since Rf is commonly either inflation or t-notes or something, what this most accurately represents in layman terms is your inflation-adjusted rate of return. You can't simply say "I could invest in another real estate deal at 10%, so my Rf is 10%". That doesn't make sense since that investment is not risk free. You are referring to Opportunity Cost when you say that. I personally find the risk free metric to be mostly useless.
- Cost of Capital: when you compare your deal against WACC, this is return rate of your equity within an individual deal, after factoring out the payback of all debts and equity partners
- Opportunity Cost: when you compare your deal against the opportunity cost of similar deals or any other investment you could potentially make, this tells you whether or not it makes sense from a pure return perspective to invest in one type of asset or another.
Super basic example below where you buy a 10% return property, and take out a 4% loan at 60% LTV and gather equity for a portion of the remainder 25% of value @ 8% and then comparing the return of your equity against inflation and an opportunity cost investment such as the stock market returning 7%:
Note that you compare the rf or inflation and the opportunity cost against your personal equity contribution. Note that the most important number here is the 37% personal return on your own equity.
That rate of return is 35% when adjusted for inflation and 28% better than investing in the stock market over the same period, but really... who cares? This is just spreadsheet shenanigans and has little bearing on your decisions for making or managing a deal in the real world.