Okay, here's another way to look at it with numbers:
Tax deferred account assumptions:
Accumulation phase - $2000 per year contributed for 30 years
7% earnings each year
untaxed
Distribution phase - $2000 per year withdrawn for 30 years
7% earnings each year
withdrawals taxed at 28%
Result - total account balance after 60 years = $1,222,774
Taxable account assumptions:
Accumulation phase - $2000 per year contributed for 30 years
7% earnings each year
earnings taxed at X%
Distribution phase - $2000 per year withdrawn for 30 years
7% earnings each year
earnings taxed at X%
Result - The value of X that results in a total account balance after 60 years of $1,222,774 = 9.75%
Tax deferred account assumptions:
Accumulation phase - $2000 per year contributed for 30 years
7% earnings each year
untaxed
Distribution phase - $2000 per year withdrawn for 30 years
7% earnings each year
withdrawals taxed at 28%
Result - total account balance after 60 years = $1,222,774
Taxable account assumptions:
Accumulation phase - $2000 per year contributed for 30 years
7% earnings each year
earnings taxed at X%
Distribution phase - $2000 per year withdrawn for 30 years
7% earnings each year
earnings taxed at X%
Result - The value of X that results in a total account balance after 60 years of $1,222,774 = 9.75%