Stack ranking is toxic and removes individuality from a given employees expectations in my opinion.

People should be qualified to give proper unbiased reviews. Just because someone is an excellent engineer does not mean they are good at understanding other people's expectations and work outputs.

I worked at a company that had no 'managers' just the owner, and everyone else. I hated that I had no real way to settle disputes and every single disagreement has to ultimately be resolved by the literal one person who was in charge.

I think there is merit to flat structures, but I don't think the extreme is always the way to go.