I insist that it is 100% meaningless comparing characteristics or qualities between individual instruments by individual judgement at a distance and when dealing with various ages of technical devices.
What apple is your favourite? What bike? What car? So what - why? We certainly have lots of individual opinions about instruments of 'ours' and 'others' but where can that bring us? It is well known among musicians using whatever instruments that for often completely unexplainable reasons even massproduced instruments from the same "batch" of production may come out with differently perceived "sound" or "response" - not to speak of "soul" - then one really gets lost...
It seems to be forgotten many times that concertinas like any other squeezeboxes are mechanical gadgets, subjects to wear and tear and ageing and continual need for reconditioning and *change* over time.
Or do they *mature* and get better with time as fiddlers may believe their fiddles do...