Perfection doesn't exist, but you can measure outcomes. For example, how quickly users are able to complete a certain task, or how many mistakes they make while trying to complete a certain task, etc.

Based on the measurement of these outcomes you can absolutely say whether an interface is better or worse than another.

Anyone in software design in the 90s/early 00s was quite familiar with this subfield of human factors. Very few people making software today are. As vibe coded UIs become more and more widespread, it's only going to get worse.