I acknowledge that they're not planets but I don't think the Garganta is infinite.
The Garganta also in't the universe since it's apparently just a void made of Reishi.
That's the thing the Garganta doesn't need to be infinite to be universal sized. Regarding the term "universe" in Bleach likely refers to everything, as in the Bleach Universe is the Garganta, Dangai, Hell, Three Realms, and Valley of Screams. They call the Three Realms, "realms" so WotL is not the entire Bleach Universe, even if the WotL is supposed to mirror our IRL Universe. The Garganta is still a part of the Bleach Universe, and going by the poitn 2 TOAA mentioned, it would qualify for universal size. Then going by Isshin and SAFWY it is a spacetime, thus making the Garganta a universal sized spacetime.
What is the size of Hueco Mundo, WotL, and SS?
Regarding all realms we have this statement: “
If the world of the living and the Soul Society could be likened to planets…” that
if meaning that they are in fact not planets.
Hueco Mundo
We know HM has a planet and moon. There's a promotional statement that says the sands are endless, so if you wanted to take that at face value you could argue HM is infinite (not at all what I'm arguing). So we know HM is a realm that is potentially unquanifiably larger than a planet with an orbiting moon.
WotL and SS
We know the realms are stated parallel. We are shown that SS has a starry sky. Gremmy is capable of imagining a small galaxy, meaning he has to have seen a small galaxy before as the imagination is just an amalgamation of everything you've seen. We also know the Kon knows what galaxies are. Both of those imply that galaxies are a thing that exists and are common knowledge. Thus it is extremely probable that these realms contain galaxies. We also know the Realm: WotL is based on our IRL world/universe. Couple all those together, and you get that these realms are most likely universal in size.
I see Matthew arguing that the WotL isn't the entire Bleach Universe thus it can't be universal in size. Why? You're speaking like the entire Bleach Universe can only be as big as our IRL Universe. That simply is not the case. Bleach's Universe can be bigger than our IRL Universe.