Nope, not wrong. Inflation can and does erode that initial ROI significantly over time. I understand where you are coming from, but that 80% ROI is only on 5% of your earnings and isn't the return it should be. You are still missing the time component along with taxes. Here's how much value the dollar has lost over the years:
2010: 31% - what cost $1 would cost $1.45 today - 1/3 of your 401K money is gone today. MM avg 0.17% (TOTAL LOSER)
2000: 45% - what cost $1 would cost $1.83 today - almost 1/2 of your money is gone today. MM avg 5.89%
1995: 52% - what cost $1 would cost $2.07 today - just above 1/2 of your money is gone today. MM avg was 5.48%
1980: 74% - what cost $1 would cost $3.83 today - 3/4 of your money is gone today. (401K first opened) MM avg 12.68%.
See the problem? And the kicker is that the 80% ROI in your example is ONLY on 5% of your earnings. The longer you live the more of that you lose to inflation, and you STILL have to pay taxes on top of that when you pull it out. This is the price of monetary inflation that our elected officials have burdened us with. Inflation over time is eroding the purchasing power in real terms.
Then assume you retire and pull in $80K annually from your traditional 401K, which is not too shabby all things considered. The tax rate for that is 19% after calculating the progressive tax ladder, which knocks a hole in the money market returns and may even eat into your principal in real terms causing a loss. So you get $64.7K annually after tax - $5400 per month.
-----------------------
My point is that SS is a racket, we all know that. But the 401K is not without its problems either and must be actively managed.