I think it would be much more interesting to use a personal rate that represents the highest return you could get on an almost risk free deal.
Let's say bonds give 2% for 20yrs, but if you could loan someone a lot of money with which he wants to buy a real estate portfolio, where he would pay 3% interest rate and the LTV is only 10%. Then I would think using 3% as your RFR would be more fair.
The more money and connections you have, the more opportunities to get into deals that are close to risk free and might give better returns than bonds.
And maybe there are different risk free rates per type of asset.
Because of the amount of money involved in some deals, 5% close to risk free deals can be done in buying/selling expensive art, while in real estate you can might be able to secure a 30 year loan for 2% on 500k which is perfectly high end and A+++ location, have it rented out. Sell 90% equity to someone who is willing to accept a 4% return (so 28k in costs in total) while renting it out for 30k. This would be a 4% ROE (just to give some examples).

I think using the risk free rated based on bonds is just a market practice because it's easy, convenient, uniform and understandable for everyone involved in the deal. But theoretically it's just a shortcut