I don’t understand either. If you do the $10,000 a year distribution and put it in a Roth IRA (convert it) it won’t contribute to your future taxable investments and also will reduce your RMD. You pay the same taxes on the distribution whether it’s a Roth conversion or not. It has the same impact on your IRMAA the year of distribution (well 2 years later actually).
IRMAA starts at $194,000 MAGI (AGI plus tax exempt interest) for MFJ. Is $10,000 a year distribution going to put you over that threshold? Maybe not. That’s what you would have to figure out. You’d have to pay more taxes now, instead of paying more taxes on a larger RMD later. That’s the trade off people try to make.
My point was that if you are going to do IRA distributions starting at age 65 to try to reduce future RMDs, but you are going to invest that money, you might as well put it in a Roth IRA and invest it there, so as not to increase your future taxable income even more, which also has an impact on future IRMAA if you cross the threshold.