For point 2: I always got the impression that they did blip out when summoned. There’s hundreds of them out there, but they’ve had thousands of years. And while we view it as imprisoned, they say they’re keeping them safe (and from hurting themselves possibly I think, but I may be misremembering that bit). So they’re stopping them from wandering around by keeping them locked up, but it’s not trying to keep them all there forever. They just feel honor bound to take care of them. That’s their ultimate goal, not to round them up.

On top of that, I’m not sure, like Syl when she’s just being her little blue self hanging out with Kaladin is also in Shadesmar at the same time. I don’t think it’s like with lower spren where we’re getting a peek at them on the other side. I think they’re all the way over. Otherwise, in Oathbringer we probably would have seen Timbre, Ivory, and maybe Wyndle and Glys just hanging out on the cognitive side around Theylan City when Kaladin and the gang showed up. But it hasn’t been verified, so who knows? Sanderson is pretty good at coming up with good reasons for stuff in retrospect.