Yes, it's complicated. You can come up with edge cases that show whatever outcome you want to show. Just the fact that it is not hard to come up with cases that can prove different outcomes kind of demonstrates that there is no right "best" answer.

The debates about when to start SS usually implicitly presume that they have a lot of money.
- It doesn't make sense to start SS while you are under FRA and still working.
- You have to have a portfolio big enough that you can live off of it and don't need SS money.

First world problems.

You're right if you look at just the difference in tax rates, that's not a ton of money.

Yup. That was my point. In the big picture it's one of the small stuff we shouldn't sweat. Even the "best" answer isn't very much better comparatively.
Having to pay tax on an additional $186,000 income -- with on a $4.9 million IRA -- just isn't even close to a life changing amount. Heck, the $4.9M account value swings more than $9,100 every day.



But the key point is they are paying taxes on money they didn't need or want.
The IRS sees it differently. The IRS says "Hey, you had some income XX years ago that you owed taxes on, and we let you defer paying the tax until now. In essence, we let you hold that tax and invest it for us. Now we want it back."
You _owe_ the tax. They don't mind if you pay it in the year you earned the money or decades later. But they *do* intend to collect it.

That doesn't say I like it, just that that is the way it is.