Not that it's a competition, but I kinda burned out on SM2 before finishing it ... then the GoW DLC was made available and I checked it out. And it was instantly far more fun to me than SM2 was. And even though it kinda looks like an upscaled PS4 game, I kinda think it looks better than SM2 too ... just the detail and architecture present in the levels. It just has such an incredible scope, and it's an interesting setting. And the music is better. And the writing and voice acting is better. It's just ... better.
So yeah they could definitely keep changing mythologies and change up the game formula a bit while keeping the core function recognizable. I think Valhalla is always way better without Atreus.
I don't know if it's "the best" PS IP, but it's obviously one of the top few, and I think at that level it just kinda comes down to player preference.