Well, you bring up interesting points. Returns have averaged much more than 10% in the last several years in many sectors on the market. Broad indexes too, like the S&P 500 have done very well in the last 5 years. Of course if you stick with the bond and money markets you are looking at near-zero returns (maybe even negative real rates after inflation). From that perspective a 10% looks too high (yes, in a finance class we can discuss risk premiums and that 10% may be too high, given historical premia and models like the CAPM). But, in terms of opportunity costs, the better metric at this point (given that the money was paid in December 2020) is the return on a less volatile equity index (like the S&P 500: 1Yr return 18.70%; the 5 YR HPR was more than 98%) because we are in a low interest rate environment. I am very confident that investors in ETFs (or mutual funds) will easily average more than 10% annualized if they mimic this index.
Yes, you have to take into account the differential taxes (that too depends on Biden tax hike). Like I said, this is why you cannot make a good guess unless you have the exact payment schedule on the original contract. I don't have it. But, I can then tell you with great accuracy what would be the better option if I had it. Anyway, RT is clueless and probably made the wrong call.