I think its probably taking the approximately 21 years you get with the sentence with maximum good conduct time reduction, and also assuming credit for time served after his bail was revoked.
That is a big difference. You can live a pretty good 15 or so years if you get out at 60. Considering that his parents are well off he will inherit some.
Milken got a sentence reduction for cooperation with prosecutors against others. The other big fish in FTX already cooperated against SBF, who do you expect him to roll over on?
This is not correct. Federal sentences do not have parole and can be reduced by a maximum of only 15%, meaning (if that happens) SBF will serve at least 21 years and be 53 when released.
Milken was released because Trump pardoned him, which I don't think says anything about how sentencing guidelines do or should work.
He was released after a sentence reduction for cooperation with prosecutors against others decades before the pardon. Both the release and pardon occurred, but the latter was not the reason for the former.