His premise might make sense for high income earners who plan to work right up to RMD age (no chance to Roth convert during ER).
It's completely wrong if you might be eligible for refundable credits like EITC.
Contributing to traditional 401k (not IRA) increases our EITC, because it reverses the 21% phaseout (and an additional 6.3% phaseout for the 30% state EITC match). That's on top of the 10% federal and 4% state taxes deferred, and the EITC phaseout "tax" won't be recaptured at withdrawal time in retirement. In fact, the state tax won't be assessed, either, on the first $20k each of us withdraws annually in retirement and after age 59.5. So 21 + 6.3 + 10 + 4 = 41.3% bonus tax refund for contributing to traditional 401k accounts, and the possibility of only federal 10% tax on withdrawal.
And, yes, I DO save the refunds - they fund our Roth IRAs. At that point, there's no more tax advantage to be gotten from a tIRA, because we've reached zero federal tax owed (due to nonrefundable credits), and because IRA contributions can't increase EITC (IRA contributions can't lower w2 wages).