Some types of music and some arrangement clearly have 2 or more guitar parts the clearly divide into rhythm an lead duty. Instrumental music requires a lead and harmony instrument and guitar can fill both roles, and the lead/melody needs to continue as required. Artists like Clapton and Knopfler hire rhythm guitarist to play that portion of the arrangements. Maybe YOU don't see it that way but both roles can exist independently and with little overlap. Ever hear of the Grateful Dead?