Yes - I agree. That is why they will try and prove this case from 3 sides.
1. The witnesses will say, IMO, that the man they saw is the bridge guy in the video. So IMO the key to the entire case is whether the man the 3 juveniles saw was RA. Based on the PCA, I suspect RA has really hurt himself quite badly by admitted he saw a group of girls. His innocence requires not only 2 Bridge Guys, but a second groups of girls never identified.
2. The confessions (enough said) and 3. Ballistics/forensics - these help with point 1.
What is revealing IMO, is the defence's lack of interest in certain 3rd party suspects. They don't look like Bridge Guy. So the defence understands this dynamic. Realistically the man the juvenile girls saw is bridge guy - so the defence needs Bridge Guy II.
Of now of course they want to shift the focus to where the girls go from the Bridge, but IMO the whole case is decided on what happens before the Bridge. What happens from Bridge Guy on, is not in doubt IMO.