It also depends how much you're trading and what kind of ETFs. Qualified dividend rate for you would be 15%. Ordinary dividend or money from bond etfs would be 25% (and REIT ETFs? I'm not sure?). So every time you reinvest you don't have as much to reinvest whereas in the 401k it's deferred.
Also as huadpe says, it depends how much you plan to retire on. If you plan to still be in the 25% bracket (your short time frame is good as probably there won't be major changes in the tax rate, but who knows? it seems to me investment tax rates are more likely to change, but, again, who knows?), the 401k isn't helping you at all except for having more principal to invest initially. So all you have to beat is whatever the return would have given you on that .25 and then (.15)(yearly dividend)(number of years). Okay, there's a bit more to it than that but if you can't do the math then you probably can't get superior returns either. Wow, that made me sound like a real dick. Not what I intended. The point is that the tax advantage of the 401k depends on more variables that are unique to your situation than just your tax rate.