I personally feel a metal band should have this line up.
Guitarist
Drums
Bassist/vocalist
All these band that have these "rhythm guitarists" I find a waste. The power metal bands ust them effectively by using seperate riffs, dueling solo's, seperate arpeggios, but for most of metal, bands just have their rhythm guitarist play all the roots of the lead. When you have a guitarist doing that, it totally drowns out the bass, and you might as well not even have a bassist then.
I think the lineup should always be that three, and the only genre of metal that needs a rhythm guitarist is power metal, and avant garde bands.