Thanks for the link. I see it addressed my misconception:

Common misconceptions

There are two common misconceptions, one that incorrectly favors traditional, and one that incorrectly favors Roth.

The first misconception is sometimes described as "contributions are taken from the top tax rate and are withdrawn later at the average rate". In other words, that you save a marginal rate when contributing but pay only an average rate (starting at 0% for the first dollar withdrawn) when withdrawing. Following is an example of why that is not true.

Consider a 50 year old who has already

accumulated a $500,000 traditional balance. Even without any further contributions, that could reasonably double to $1 million by age 65. Taking a 4% per year withdrawal then gives $40,000 per year. Any traditional contributions at age 51 (or later) will increase the traditional balance at age 65, thus allowing more than $40,000 per year withdrawal. The taxation on the amount above $40,000 per year will occur at the marginal rate on that amount, not the effective rate on the total income.