I'll stimulate this discussion.
The comparison shots are not ideal.
Perhaps (as in, please do) take them straight on lined up with a ruler or graph paper, or some such set up.
Bird's eye views and action poses are not helping.
From what's visible of the difference between the space marines, sorry games workshop's space marines (don't want confusion with space marines of anybody else who wants some), and the less yelly, not so topless chaps without shields, I am reminded.
The Unit, "we're not worthy", had an episode (the first? "Wash your mouth out") where Jonas ran through a plane stuck on the tarmac hijacked. He had only a pistol and took out the hijackers one by one in quick succession.
Apparently people on set wondered why he wasn't wearing any armour or vest. The production head/s (military folk) explained that the idea is not to get shot.
Which gets even weirder when you see computer game footage of GW space marines jumping and rolling around like the love child of a ninja and captian Kirk.
I veiw them moving more like robocop or a T-800. Robo looks pretty legit, and he isn't even as heavily armoured.
Yet, he is slow and armoured, he takes many hits, but has the fire power "to get the job done."
I don't feel the marines dodging bullets is in keeping with either their character, role, or armour.