If you want to better understand the ‘secret’ of PJ’s AI, I highly recommend listening to this episode of https://tonebenderspodcast.com/193-the-sound-of-the-beatles-get-back/
I think AI is great on these kind of things and will only get better. The ‘Get Back’ results sounds astounding to me, but i admit I have not used spleeter myself. I’m happy to see this kind of development in the DAW world after years of ‘new cabinet convolution models’ 
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