Agreed that the neocortex uses fewer layers because of looping - I also suspect it's partly because neurons are more complex than the neurons used in ANNs, so in principle they should be capable of more sophisticated computation in a single forward pass (especially considering that handling multiple neurotransmitters could mean superposed functions).
The point about there being one correct way to model something does seem backed up by the Platonic Representation hypothesis (https://arxiv.org/pdf/2405.07987). I've even seem some work that shows you can find a bijective map between the latent spaces of different transformers (https://arxiv.org/pdf/2505.12540).
Your point about Finsler spaces is fascinating - I hadn't come across the term before. It'd be interesting to see if there's work that specifically allows latents to exhibit that kind of directional metric behaviour, and whether that improves generalisation or something.
On the entire brain being dedicated to prediction, that's more of a high-level comment. I was thinking of work like Andy Clark on predictive processing, which suggests that even regions of the brain which we think of as receptive (eg. the visual cortex) may be implementing a generative/predictive model which is corrected by sensory input.