A traditional IRA deduction is worth your marginal rate today. A Roth withdrawal is worth your marginal rate in retirement. If those rates were identical, the two accounts would produce the same after-tax result - the mathematics are symmetric.
They are rarely identical. Early-career savers in the 12% or 22% bracket usually expect higher rates later, which favours the Roth. Peak-earning professionals in the 32% or 35% bracket usually expect lower rates in retirement, which favours the deduction.
A few asymmetries tilt the scale further: Roth accounts have no required minimum distributions during the original owner's lifetime, they give heirs a decade of tax-free growth, and they provide a tax-rate hedge if legislation changes. Most households benefit from holding some of each.