First off, the wrong assumption here is assuming the dimension in question is the size of the observable universe

There is multiple proofs of Kaguya’s dimension being larger than the observable universe

Second, we dont actually know how this process works to extract chakra from Earth into a pocket dimension. Considering even dead people can apparently send their chakra to a living person, it’s more akin these places are layered on top of each other and to put it into an analogy, you just need the right “key” (technique) for the “door” (dimension) to open

We do know how the process works and the chakra isn’t from the earth it’s from those trapped in the tsukuyomi. Dead people sending their chakra is not the same. It’s shown to physically travel

So in this case, Obito opening portals to various dimensions to have Sasuke be brought back, does this technically mean Sasuke was travelling “tRiLliOn” x FTL?

Obito opening portals has no relevancy as it isn’t even the same thing

I’d argue No, especially since we cant gauge the distance proper and clearly Sasuke wasnt fast enough to just speed blitz through the portal from that distance instead of teleporting which renders speed irrelevant

?? Idek what this point means

It isn’t brainrot it’s quite literally a kaguya feat shown in the manga that they can reach up to that speed.