I feel like the dog brain studies are at least fairly strong evidence that quite a bit of information is preserved. The absence of an independent validation is largely down to the poor mainstream perception of cryonics. It's not that Alcor is campaigning to cover up contrary studies - it's that nobody cares enough to do them. Vis-a-vis the use of dogs, there actually aren't that many animals with comparable brain volume to humans. I mean, if you want to find an IRB that'll let you decorticate a giraffe, be my guest. Dogs are a decent analog, under the circumstances. They're not so much smaller you'd expect drastically different results.

Dog brains are 20 times smaller than human brains: 70 g vs 1,300 - 1,400 g. Given the square-cube law, this means that dog brains have a much higher surface to mass ratio, therefore they can be cooled faster without cracking and using a lower concentration of cryoprotectant. (Cow brains, on the other hand, are just 3 times smaller than human brains and about the same size of chimp brains, hence you don't need to experiment on an exotic animal to get more comparable results).

And we don't know how much information was preserved anyway.

And the only studies being made by an organization that has ideological and financial stakes in the outcome is a big problem. As far as we know, they could have selected the best micrographs, hiding under the rug those that showed substantial damage.
Cryonics organization should encourage independent replication instead or playing the victim.

In any case, if this guy wants to claim that cryonics doesn't preserve fine-grained brain detail, he can do the experiment and prove it.

The default position is that cryonics doesn't work. It's the proponents that have the burden of providing evidence that it works. ALCOR dog brain studies are weak for the aforementioned reasons.