I have both,and if we are comparing just sounds and styles,I think the SX900 is right up there with the Pa4X. Styles are very subjective,but enjoy the variation between them when applied to similar songs. I used to be a gigging musician before the pandemic hit,and there are advantages in the Pa4X,as is expected.
Especially,at it's price point,I think the Sx900 is great.
Bernie