I'd be really surprised if the free steering arrow was no flinch; it sounds like just a weak hit to me which is really perfect. I'm envisioning a hit, a very tiny amount of hitstun and almost no launch, and a small amount of damage. That would be pretty crummy on-stage, but against a recovering opponent, it could be a very large obstacle since every hit they take disrupts their recovery, a weak launch means the net effect of getting hit is probably falling (see also: getting hit by a Sheik needle off-stage), and the peril of an off-stage position will likely make evading a precisely steerable arrow difficult. Of course, we'll need to actually see it in action to know its true dynamics, but based on the description, this is the sort of powerful gameplay dynamic I'm imagining.
As per the Guardian Orbitars, they weren't used much in the demo gameplay I saw (and Pit as seldom picked in that as well, despite seeming pretty good), but my rough impression of them is that they seem like Pit's old down special except two directional. The Mirror Shield was honestly an incredibly marginal move in Brawl; the start-up time meant that it didn't deflect close and quick attacks well, the cooldown often made punishing after a successful block hard, using the move really killed your ability to stay mobile which is very important for Pit, and throwing it out at the wrong time was pretty easily punished by grab. We had a strong Pit player in this area back in the day, and he used the Mirror Shield almost never. The move has a lot of room to improve and still be a marginal move so I'm not terribly worried about the risks of it covering a much bigger area; if anything, I'm more interested in what variations the Guardian Orbitars have since as we saw with Rosalina a defensive down special could very well have offensively useful variations.