I was going through the section with a group earlier on, as the group started deteriorating I thought to myself if it was possible to complete this section solo, i saw on a twitch video of a group who were doing the raid for the first time and had accidentally created the bridge with no one defending the totems so I decided to give it a try, this was my 7th attempt at it. If you have any questions I will gladly answer them. Edit: I tried it with a friend today, only one person needs to be alive on the other end of the bridge for the waves to start coming, when I killed the two ogres the bridge appeared and my friend could just walk across it, my thinking is Bungie thought this is a possible strategy why else would they spawn the bridge after you complete this part. Maybe for the hard version everyone has to cross the bridge before the waves actually start spawning.