Oh yeah, you're definitely right in that regard, I got that feeling out of the units as well. They do feel rather otherworldly and it's sorta meant to make them seem like these angelic saviors. Still not too fond from what I've seen of the two units I mentioned, I feel they could've still been that but made better, the rest has the same aesthetic but nails it, whilst the other two leans more on the otherworldly side of kinda looking silly. But as said, the shots of them are very hard to get a good look.
That said it's not that I'm opposed to such designs, imo I find Space Marines and Terrans rather bland and always have, although I'm kinda fond of the newer SM models like Primaris that gives more depth to their aesthetic. But I've always loved say Tau by aesthetics, I find most of their design quite functional and down to earth (even if I've heard people say they look out of place and anime) whilst still unique, futuristic and alien, and their mechs as well, whilst I've not been too fond of Eldar's aesthetics even if they make sense and nail the otherworldly/alien side.
Maybe it's the more rounded and oval shapes with simplified looks which I dislike in futuristic designs, as opposed to ones with more edges and depth to it, or layers within say armor where you can distinguish parts and layers of it where it feels functional and not just to look otherworldly for the sake of it. Though perhaps I'd be more open for it if Oathbound or say Eldar actually were more alien and not humans/elves, as I do like Protoss' design, so maybe I might have a problem they aren't aliens afterall!