Alien superhero princess
Yeah I've heard good things about Huey but I doubt he'll be good enough to compare to TTYD or SPMYou might not like Kersti but don't throw Color Splash into that lump because Huey is a genuinely great character.
Also you give SPM's partners too much credit, all main party members except Tippi were pre-established characters with personalities already set in stone. Tippi has some pretty great character development but she's really the only one.
I stand by my praise to SPM's partners. Tippi is probably THE best partner out of all the Mario games I have played. As for the others, they were genuinely excellent, they stay true to their presentation to their roles in other games and build on them in lots of other ways. Having Bowser and Peach as major protagonists and playable characters at the same time is quite rare in the Mario franchise (though by no means a one off) and Luigi was really cool and brave especially in 8-3. Sure the latter three weren't entirely original like the partners in the first two but considering how non-Mario 90% of this game feels like I'm not complaining. As I have said in this thread previously, they feel like a sole point of familiarity, comfort, and humour in a highly atmospheric strange world.