No. Its for feedback suppression. It involves playing with phase and eq. Sometimes the second ( or even a third) mic was backwards for this reason ( see Woodstock footage). Microphone gain before feedback was not so great back in those days ( if you look close at the product lit for the Shure SM58 you will still see how they draw attention to it having a high gain before feedback, this is a legacy of that era and nobody really cares anymore). On shittier mixers with weak preamps double micing like that could get you the volume you wanted, but that would be smaller shittier shows.
For a broadcast feed they'd usually take the mixer output vs individual channels , but even if they did easier to use the mixers channel inserts as an improvised direct out.
Basically, every time you see a vid of a ‘live’ performance from that era, the 2( or more) mics is the tip off that it wasnt lip synched.