My perspective as someone who is mainly active in the anime/gaming fandom and gamedev space:

• Easier onboarding overall since you don’t have to bother with choosing an instance and all that
• despite starting out with less features than mastodon (no gifs, they are only getting video in the next update wth), the UI is overall more user-friendly and similar to Twitter’s
• Customizable feeds you can easily subscribe to in-app so you instantly have some content on your timeline (+ it’s easy to be found in these feeds without having to research the specific tags to use)
• Discoverability (through features and community efforts) is so much better. As someone who mainly follows artists, the last few days my TL was full of people doing artshares via quote-repost chains or sharing “starter packs” with lists of people to follow
• I have seen exactly one artshare post on mastodon so far (the japanese side seems to have it figured out a bit better, though. I regularly see tag-based artshares going around)
• meanwhile, to achieve a similar experience on mastodon I had to manually build myself different feeds in phanpy in which I’m following ~30 tags I have painfully collected to find the posts I’m interested in
• quote-retweets don’t exist yet but I kind of see the benefit now
• the stackable moderation also helps a lot

Overall, I think the main problems on Mastodon’s side are difficult onboarding and lack of actual community-building efforts. Also, the community just seems to be less welcoming for creators in general imo