Cosmologists have modelled the universe as this uniform, isotropic expanse for years in order to make their simulations easy. Not only that, they also assume gravity to be the only fundamental force that affects large scale cosmic events.
Why do they ignore electromagnetism ? Granted, it is attractive as well as repulsive, and we see the universe as net neutral. But, that does not imply it cannot have large scale effects. Another argument is, that electromagnetic events don't last as long due to neutralization.
Electromagnetism is 10^40 times stronger than gravity at the same distance, have you tried asking whether it compensates for the short duration events ? Have you tried to model a universe less empty, filled with dark plasma and Birkeland currents ? It is but funny that if the universe was more dense with plasma than we think [something Voyager has hinted at], plasma in between would distort electromagnetic signals we get from the interstellar medium ! Which would imply our understanding is based on corrupted data. The CMB being quite uniform isn't how you dodge this, even that has been shown to be possible due to EMG distribution.
Finally cosmologists converge to - "But our models and simulation show plasma is irrelevant at cosmic scales !", and then when you look at their model, its one that plasma physicists would commit homicides over, treating plasma as this uniform, linear, predictable fluid, when it is clearly not.
You know how Z-pinch is central to star formation, not all the work of pure gravity. Is it not time to model the universe with a more plasma centric approach, especially when the JWST has already been humiliating your gravity centric isotropic models ?
I'm again going to mention stochastic topological theories, as they allow much more interesting large scale phenomenon that can explain galaxy rotation curves, either we try that or remain stuck in this nightmare.
Move on from a model that needs 95% of the universe be made of unknown stuff.