It’s very reasonable to conclude the universe is finite in size since it is finite in age. How could the universe be infinite in size if it originated from a singularity a finite number of years ago (~ 13.7 billion years)? Even if it expanded at a finite speed that is faster than the speed of light, the size would still be finite,
Since no definitive answer to that question exists yet, ad hoc and hypothetical scenarios are necessary until there is some evidence to support one explanation over the other, and we don’t have that evidence yet as far as I know.
The white hole model flows from our observations without the need to introduce a multitude of ad hoc additions. If we take our observations at face value and don’t introduce extraneous hypothetical explanations, I believe the white hole model makes sense.
To recap the white hole model so far. We assume the entire universe started in a small volume. By definition, this would be a white/black hole. During the expansion of the universe, the event horizon would collapse as matter/energy moves apart. This would cause gravitational red-shifting. The isotropic nature of the redshifting is due to us being at/near the center of the universe.
On the whole, the explanation is reasonable. But there is of course one giant problem with this that secularists will not accept and that is we occupy a privileged position in the universe. But, since I’ve already presented evidence to support this and no counter evidence has been presented, this also is reasonable to hold.