I seem to be one of the few who's not a fan of Piranha Plant. I think he's about limiting the option movements of your opponent with his B and side B. They're good for getting your opponents to shield or jump at the ledge, respectively. But I don't see anything special about the plant otherwise.
My only worry is the stage builder. Testing out spirits had no option to use custom control mapping and I fear stage builder's test mode won't have it either. It's not like a huge issue but a minor quality of life thing I hope they'll fix/consider at some point.
I think that Joker looks like a lot of fun. I haven't played P5 but have watched a lot of gameplay and am really excited for it. my favorite part of joker is the victory intro and how it's just like the victory animation in P5. also the stage looks sick and I love how it changes colors depending on the song!