OK. Here is a photo of how I connect all the ESC’s to the XT90 plug whilst keeping it just to one side of drone. (Please excuse dirt, but I am actually using it here and there) 
Regarding PDB: I think manufacturers often supply those as it is convenient and neat connecting everything that way. But not really giving it any thought as to the technical consequences. Also it brings the risk of hairline cracks forming after a hard landing which can spell disaster at a later stage. - As some out there have already discovered the hard way.
I personally would just use it as part of the frame, but connect everything in a different way.