After quite some time of thinking about it, I believe my suspicion about what the cosmology is like may actually be true.
With the airing of UGF, we were given insights as to what Dimensions may actually mean in the context of the series.
Yullian was the one whose statement was important, which is: "Does that mean he travel to other universes in different dimensions?" (Not galaxies in different dimensions as the subtitles, official they may be, has stated)
Because of that, I suspected that the series may actually be using dimensionality in a surprisingly reasonable manner in that just as there are many 3-dimensional universes, there are many greater 4-dimensional manifolds that holds these universes inside of them. This isn't the only time dimensions are stated as being contextually different than universe as in Episode 6, Ken appoints Zero to be the recruiter because of his ability to travel between dimensions, which he uses to travel to universes such as those of U40 and Ayaka City's universes.
Tregear also gives out similar descriptions on the mechanics of cross-universal traveling. He describes his ability to resurrect as being physically replaced by alternative versions of himself from other dimensions as opposed to universes. How this is relevant brings us all the way back to Zero's first Gaiden with the statement by Captain Hyuga.
"There is not just one universe. There are many dimensions where the exact same space(universe works too), the same Earth with the same humans exist."
宇宙は一つじゃない。次元を隔てて、同じ宇宙、同じ地球、同じ人間が平行して無数に存在する。For easy translating purposes later on.
Not only that, but just before this, he specifically states the multiverse as "多次元宇宙", which could literally translate into multidimensional universe. The focal versions of Hyuga and Rei were also described as being from a different dimension. This supports the idea that there are many more 4-dimensional hyperspaces that also contains countless amounts of universes inside of them. Even the Zero movie which finally explores the multiverse somewhat extensively, only mentions the other bubbles as being alternate universes, as opposed to dimensions.
In conclusion, based on this, the cosmology of Ultra Series might actually be Countless x several due to the fact that there are multiple,, constantly expanding 4-dimensional hyperspaces containing countless amounts of universes inside. And Alien Salome's experiments were going to wipe out all of that.
Edit: I call it 4D hyperspace to differentiate it from the 4D Continuum that is already what a universe is here. And to expand on why I think a dimension is completely separate and greater than universe, think of it as being similar to how we perceive our own 3-Dimensional world, such as how there are multiple 3-Dimensional celestial bodies containing lifeforms within the confines of our 4-Dimensional space-time. In a similar manner, these 4D hyperspaces are like planets in a greater space confined within a 5th Dimensional plane. Also, this may actually explain how shows like Great, Powered, Neos/Seven 21 and Max's could happen despite them insisting that they can't go to other universes even though they can; it's because the other universes that needs saving are completely out of their own hyperspace. Speaking of hyperspace, in X, even though Gourman refers to their universe as being the 3rd dimension, they still talk about super space-time theory which was possibly hinting to other dimensions.
To be honest, I feel like Kamen Rider was also going for something similar, but I'm still weighing my choices here. There could be a possibility that this may be moot to some point because destroying multiple structures of similar scale might not work.
Also, I hate having brain blasts during the downtimes of the threads because it makes me look like a nutjob. I have a life, I swear.
