Unless I'm off on my math
You are, sorry.
It's true that increased time should lead to increased dollar returns, but that doesn't matter. The rate matters, and the rate is the same on both ends.
Suppose you are in the 25% tax bracket and you have $1000 to contribute today. If you contribute to a Roth, you only get to put in $750, whereas if you contribute to the regular 401 you can put in the full $1000 - that's $750 plus $250.
However long you have the account before you pull it out, you are earning whatever return you get - call it "r". So in a regular 401 your finally tally is (750+250) times r = 1000r, but if you'd used a Roth instead you'd have 750r.
If you are still in the same bracket, now you get to pay 25% tax in the regular withdrawal. What's 25% of 1000r? 250r. So you're right back to square one.
Notice this is true no matter how many years are involved. The only variable here is whether you pay the same tax rate.