I'm not sure I understand what the question is. If you have a choice to either put money in a tax-advantaged account or a taxable account, it's usually better to put it in the tax-advantaged account. One of those scenarios is when you expect to have a lower taxable income in retirement than you make now.
One way people do the Roth ladder:
Age 45: Live on Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
Age 46: Live on Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
Age 47: Live on Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
Age 48: Live on Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
Age 49: Live on Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
Age 50: Live on Roth conversion, Roth IRA contributions and/or taxable savings, and do a conversion of the amount you want to spend 5 years later
etc
Since you want to retire in 20 years, you'll probably have quite a lot of Roth contributions and taxable savings by then.