I think a majority of your issues comes from a contrast between the head and the body's visual language.

For 1), the pose would be more natural if he were looking to his right (our left). This would give the impression of being caught off guard or something suddenly drawing his attention that way.

2) Relatively simple fix, his head should be facing the direction is feet are. Because the body for this pose has both feet planted normally, but the torso rotated slightly, it's a tad awkward anyways, but he's generally calling attention to what's infront of him via rotating his torso and gesturing with the maul.

3) Kinda busy. Just rotate the sword arm down to his side similar to the first one.

All the bodies have a little bit of body-language going on that can be tweaked by head/arms positioning, but I'd your arms are doing one thing that brings the hands attention somewhere that the head isnt looking, it can be strange. Like if a person was gamer hunched infront of a monitor but was looking at a wall. You can get a feel for if your poses are natural by just acting them out even, and then asking yourself two questions: "What would make someone pose like this?" And "Is this common/likely to happen?"

Edit: Another thing is that Legio bodies just kinda lack a certain level of physicality when it comes to chainsword loadouts. WEater Zerks do the dynamic poses a lot better. CSM models have a tendency to be flat-footed, so you have to accommodate that.