LG-15

Leaving aside the choice of materials, the nature of the sound of a given instrument is governed by the size and shape of the body and bracing but is heavily influenced by the way energy is transmitted to the instrument.

Standard guitar design...bridge with push pins
Strings originate at the headstock, land on a thin saddle that is trapped in a slot in a flat bridge and descend into the body, captured by push-pins.  If you think about the distribution of energy, the strings are simply trying to rip the top off the guitar.  The soundboard is being excited by the pull both in the direction of the headstock and laterally as the bridge is being jerked sideways.  Think of panning for gold... swishing a pan sideways and rocking up and down.    Stability of this system depends on correctly placed bracing but older instruments eventually are affected by these forces and bridgework needs to be done.
 

Archtops and Hybrids are "Tailpiece" guitars
Strings originate at the headstock, land on the bridge and end at the tailpiece. 
In this case the distribution of energy is almost entirely downward.  The strings exert an up and down force on the soundboard.  The path of the string's pull describes a shallow triangle... the apex is the top of the bridge and the base of the triangle is the guitar body.  Forces present are, in a sense, holding the guitar together as opposed to trying to tear it apart.

Drawing a contrast...
For a standard "Push-Pin"guitar, sound must find its way through a saddle, bridge and six pins... a total of eight "things" that can effect sound. 
For a Tailpiece guitar with a one-piece carved bridge, sound goes directly into the soundboard with nothing else in the way.
 

Could be...
Could be that the radical difference in the way the two guitar types excite the soundboard is the reason a push-pin guitar is much more an overtone generator.  A Tailpiece guitar produces sound that is more well-defined (sometimes called "dry") lacking that "first batch" of overtones.
Both guitars will, of course, be generating their own overtones as a result of the other aspects of construction. 


Part Two...Archtops and Hybrids