Its actually impossible to compare set neck, neck through and bolt-on really when it comes to sound and sustain blablablablba
Brain washing and marketing however seams to work very well
Why? very simple:
are all 3 instrument built with exactly the same wood, from the same board and have the exact same density? Do all 3 instrument share exactly the same specifications, settings, string guages etc?
The reply is NO its impossible....
If you want to compare you would have to do something which does not yet exist, this would be to actually clone a tree 3 times and use exactly 3 times the exact pieces of wood which will be cut exactly the same on all 3 guitars, same applies to the fingerboard etc...
Then and only then will you be able to give a real judgement....
Also, how do we define sustain? I have never seen a rule telling that sustain MUST be more then 15 seconds!?!?!?
This is all marketing poo poo...
The thing to do is to use what you like and what suits your building style and philosophy and perfect it.... That's really it
BTW historically bolt-on is by far the oldest way of attaching a neck on a musical instrument, stradivarius was using 3 nails to attach the necks on his violons in the baroque period Most lute makers use a big screw to attach the necks....