As ever its personal preference.
The bigger the frame the less maneuverable it is on corners and in the air.
A low top tube and stand over height allows to get much lower and in my opinion thats more fun.
I’m 5’11 and my do it all frame is just over 16″ with a top tube length of 22.5″ – I have never really run a saddle super high and your muscles get used to it, when climbing my saddle can go up just above stem height no probs.
I agree that a fitted frame has its benefits but at the expense of fun on the downhill (the bits I’m interested in) its worth it.
In my experience anything over 17″ isn’t really ‘chuckable’