Those were pretty much my own takeaways as well. Maybe there is enough wiggle room in there to make the case that case that mythical zoans are creatures that they don't know if they ever existed. Kaido's fruit is still a bit weird though. Since dragons did in fact exist in one piece. Maybe his specific variety of dragon is the one that didn't exist hence the mythical bit.Punk Hazard's "SAD" is a liquid that mixes the lineage factors of various animals.
It seems that the Lineage Factor is indeed just another term for DNA, and SAD is merely the result of DNA extraction.
According to Shinobu, only 10% of SMILE fruits work because the formula is incomplete. But why does the failed ones make a person smile permanently?
"Dressrosa's "SMILE" factory allows plants to absorb SAD, and grow up with peculiar patterns. One tenth of the fruit imported to Wano Country can give animal abilities. That is to say, it has nothing to do with genuine "devil fruit".
Does this mean that despite the similarity, SMILE nature is completely different from regular Devil Fruits?
If that's the case, then they are essentially fake Devil Fruits.
"and the lineage factor can only be extracted from existing creatures, so any "mythical zoan", "logia" or "paramecia" abilities cannot be produced.
This imply that Mythical Zoans are creatures that don't exist, meaning that something like a phoenix doesn't exist in One Piece world.
I also think this SBS hints at something bigger. We know caesar used existing DNA for his smiles. Vegapunk also used kaido's DNA to form his dragon fruit which he still regarded as a failure (which worked much better than kaido's smiles). So... I think this hints at technology back in the day being so advanced that they could create or write lineage factors pretty much from scratch. Obviously there most devil fruits can't be based on living creatures in general. So the alternative would be that they could make mutations they wanted. It's possible zoans and ancient zoans were based on existing dna though. In this context its also possible that regardless of whether mythical creatures existed or not, since they couldn't find any of their dna they simply wrote it from scratch to make mythical zoans.