I currently invest in a Roth 401K, and part of me is thinking that I should just be going into Vanguard Index funds since the plan my company offers me doesn't

I currently invest in a Roth 401K, and part of me is thinking that I should just be going into Vanguard Index funds since the plan my company offers me doesn't have any good low cost index funds (just targeted retirement). I've been thinking that a non-Roth 401k is ultimately a bad deal because of the tax issue, besides increasing in tax brackets generally as you get older until you retire.