"But what's wrong with this?" What's wrong with this is that often times, people leave these types of comments when it's not necessary.
Leaving comments like this takes a moment of celebration and turns it to a moment of spite.
This is especially annoying when it's online. Most online spaces are algorithmically based and since algorithms like to share posts that will spread controversy, comments like that are only going to attract more people to it.
Bringing generative AI into a conversation that was started when someone wanted to share their art is just going to attract a generative AI dick rider to "erm actually..." the conversation. Bringing transphobia into a conversation that's supposed to be support of trans people will cause transphobes to enter the conversation and remind said trans person about transphobia. And so on and so forth.
If you want to show your support, keep the first half and drop the second half. Just say "you're amazing" and move on. It's a supportive message and it's still a celebration.