It’s obvious what Rundblad's skills are and why Stan likes him. Big shot, good passer. Rundblad's problem is that, like Oduya, Hammer and Leddy in 2012, is that he does not react well under pressure at all. Whether you consider it panic, or a lack of confidence, cutting down on his time makes it very difficult for him to use that great passing ability.
Part of his problem, and the reason why - unlike Hammer, Leddy or Oduya - he's probably going to top out at a #5 position, is that he doesn't have the wheels to compensate. Those guys learned to take a breath and use their feet if their their forwards weren't being responsible and affording them a good passing option. Rundblad, while certainly faster than the corpse we call Roszival, doesn't have the wheels to escape that pressure. So his two options are pass or off the glass and out. Once he gets into the offensive zone, he's pretty damn good.
Giving him consistent decent ice-time and ensuring he knows he's not getting stapled to the bench for making the kind of miscue that every other d-man on team makes here or there without penalty would be a good way to help him settle the **** down, take a breath, and make the smart play. But of course, as he's not a member of the AARP or one of Q's chosen 'boys', that's probably not going to happen.
By comparison, Roszival brings essentially nothing but size. He botches 9 out of 10 zone exits, he's too slow to keep up with even the slowest forwards in the NHL, he's constantly getting turned around and beaten out of corners by his man, and he takes a lot of hooking and holding penalties as a result of his inability to keep up. His brain is still there, which is why once in a blue moon, he'll make a great play that gives his devoted band of loyalists enough fuel to feed their delusions of his worth, but sum total, he is an anchor on this team and should not be getting anywhere near the minutes he is.