DJI video tutorials clearly state to remove the gimbal cover before flying. So what is there even to make a decision about? You either follow instructions or suffer the consequences, as a rule.
I don't think a piece of non-optical, molded plastic is going to help out anyone's photography or filming, especially if it's scratched. The camera simply is not designed to shoot through that material at all. Besides, if you can mount filter lenses on the Mavic then it must come with it's own lens filter, probably a UV filter, that is going to protect the optically-ground lens in the camera. I say leave the engineering to the experts and follow what they say about their creation unless you can prove them wrong. To me this is a real no-brainer.
The optics on the camera are cherry. The optics in the gimbal cover are toast. If they were any good for looking through, then corrective glasses would cost a helluva lot less money than they do.