Multiple POV scenes make for a very strong reading experience...So, in light of the "I" of the MC and the "I understand you" of the other character POV scenes, here's my guess:
For the OS, we can know what's in the head of most of the key people generally, what they're doing and on the surface why they're doing it, even their motivations and reactions and feelings and thoughts. And even for the more intimate relationship we have with the IC, we feel a bit distanced with him not being completely upfront with us, but still knowing what he does and thinks and how he feels, but not really the deeper WHYs.
But only the MC keeps no secrets from us. Is this how to keep the IC and multiple OS-POV as separate from the MC?
A well made antagonist/contagonist is one who has reasonable goals and intentions of his own. When I read, I enjoy knowing what the other characters are thinking and how they're responding (omniscient 3p), but wondering the "why" because it's cloaked.
The more the reader identifies with the anti-force/or counter-force, the stronger the tension and more of a dilemma. The more that is cloaked the more suspense and mystery.
But those secrets of the heart keep me moving forward, especially as they affect the MC I'm rooting for.