I'm not the best at theories (or at explaining things), but I would like to believe that Flowey is not entirely Asriel. Flowey may have Asriel's essence in him (from the dust being spread on him), but he doesn't contain Asriel's soul (which was why he couldn't feel emotions). Flowey was just a plant that gained a will to live purely with the help of determination. While he resembles Asriel, he is not the same person. Flowey is Asriel (in a way), but Asriel is not Flowey.



That's just what I think at least. I hope it made sense!