I feel like I'm missing something...?

You are, and TheDude and RewardTraveler's posts above are the only messages thread to directly address what you are missing. I will say the same thing but in a different way.

You are missing the Opportunity Cost of the money that you are paying now in taxes.

Your comparison needs to have either the Roth and Traditional accounts both on an after-tax basis or both on a pre-tax basis for equal comparison. As an example, let's say you're contributing the max this year ($17,500) to your 401k, and that you will withdraw it later and that money will have doubled to $35000. I will assume the same tax rates as you did in your example, 25% now and 15% later.

Roth:

You contribute $17,500 now. You must come up with an additional $4,375 to pay your 25% taxes now. It doubles to $35000 later. You owe no additional taxes, so you have $35000.

Total spent: $21,875, Total gained: $35,000, Total returns: 1.6x

Alternate Roth:

You only have $17,500 to invest. You must pay 25% taxes on anything you put into the Roth account, so you can't contribute it all. You contribute $14,000 to your Roth account, pay $3,5000 in taxes. You $14,000 doubles to $28,000, you withdraw it tax-free.

Total spent: $17,500, Total gained: $28,000, Total returns: 1.6x

Traditional:

You contribute $17,500 now. You owe no extra taxes. It doubles to $35,000. You withdraw it and pay 15% taxes on it ($5,250). You have $29,750.

You also have $4,375 that you did not pay in taxes. You pay 25% taxes on it, leaving you with $3,281.25. You invest it in a non-tax-advantaged account. It doubles to $6,562.50. You withdraw it and pay 15% tax on the gains, leaving you with $6,070.31.

Total spent: $21,875, Total gained: $35,820.31, Total returns: 1.64x

Alternate Traditional:

You contribute $17,500 now. It doubles to $35000 later. You withdraw it and pay 15% tax later. You have $29,750.

Total spent: $17,500, Total gained: $29,750, Total returns: 1.7x

So no, it is not in any way better in choose Roth over Traditional just because the number you pay in taxes is lower. You also have to take into account the Opportunity Cost of giving the money to the government now instead of later. Nords is correct, the only two things that make a difference here are tax rate now and tax rate in the future (assuming they don't change the laws and suddenly make Roth accounts taxable on withdrawal or something (which I find unlikely)). If your marginal tax rate is higher now than it will be in retirement, then Traditional is better. If not then Roth is better. The trick is just in predicting the future.