> Evolving eyes from light sensitive cells means that the organoid in every intermediate step should be a functional light detector that’s slightly better than the previous iteration if not the same.
This is not entirely true, because there is horizontal gene transfer, and serendipitous combinations, even of "junk" DNA. For example, eyes started off as ordinary brain cells that just happened to have a light-sensitive chemical in them: melatonin. The melatonin could have had another non-photosensing use prior to this, or it could even have been a mere byproduct of some other process.
This is not entirely true, because there is horizontal gene transfer, and serendipitous combinations, even of "junk" DNA. For example, eyes started off as ordinary brain cells that just happened to have a light-sensitive chemical in them: melatonin. The melatonin could have had another non-photosensing use prior to this, or it could even have been a mere byproduct of some other process.