Errr, well the thing is both of those musical compositions (flowey vs retina) are VERY different, Flowey is very consistent and repetitive in nature whilst retina is actually quite sporadic with deeper instrumentation on the bass in comparison, making the higher diff mapping of these compositions very different in nature too. Next of all you can't convert the style of an extra or higher into an easy diff (which is what I assume you are talking about here) since the limitations of an easy or normal are quite high in comparison, so linking an extra and trying to turn it into a normal wont work at all, only basic aesthetic themes can be carried over, and this music doesn't really need any special slider themes.
Mettaton Quiz doesn't feel like a boss to me, neither can you lose but it isn't really classified as one either. The dummy however I was planning to some time ago, but dropped due to the fact that the Dummy doesn't affect the -ending- of the game, whereas all other bosses do. I might map dummy in a separate map though.
And lastly, Flowey broken on ctb? Well I can't do much about that, I'm mapping for purely std and don't want to risk the mapping of the standard version for conversion. Of course both is better, but I would rather focus on std rather than have 50/50 for both.
Thnx for input yo