Interesting to compare these. You might get better results with a remote shutter for sure, but I'm really just blown away by that P900.
Here is a shot from the Sony a6500 with a Sigma 150-600mm taken from a tripod with a remote:
https://flic.kr/p/YYjD6C I think we lost a bit of contrast overall (though I'm not looking on a good monitor right now), but I'm really pleased with the detail on the left edge. I'd bet with a remote you could get similar results if not better ones.