Using a guy/gal that retires at 20 years with the high 3 years consisting of 2 years as a LtCol and one year as a Major vs 3 years as a LtCol.
(O-5 pay)$8,422.20 + $8,422.20 + (O-4 pay)$7,356.60 = $24,201/3 = $8,067/2 = $4,033.50 (50% of base pay)
(O-5 pay)$8,422.20/2 = $4,211.10 (50% of base pay)
OK obviously not a math major or an expert on the Top-3 retirement sysytem, yet, but it looks like only a difference of $177.60. I think it would take a little over 235 years to lose half a million dollars. Feel free to correct my logic if I am wrong.
https://militarypay.defense.gov/retirement/ad/03_highthree.html