My friend, I'm not sure you've thought through this all the way.

Historically, tax rates have gone down over time, not up. Especially in recent history.

You do pay a reduced tax in retirement because you're able to blend your income. You defer taxes on the 401k until requirement, but you pre-pay taxes on a mega backdoor/roth, so if you need 100k of income in retirement you pull 50k from 401k and 50k on the roth and only pay taxes on half of it, putting you in a lower bracket.

Having the pretax money to grow before paying taxes on it is greater than having post tax money and having less to compound.

The alternative to tax advantaged places to park your money for retirement is strictly worse than non-tax advantaged. In a 401k you pay taxes only in retirement, for roth's you pay taxes only with your paycheck. In a brokerage, you pay taxes at your paycheck and then you pay taxes on withdraw for your cost basis.