For what it's worth, my experience is that small bodied guitars are not invariably "trebly" or bright. They are not as loud as bigger guitars, but the tone can be quite full and rich. One thing to keep in mind is that a surface becomes stiffer geometrically as it shrinks. Shrink the width by half and the top becomes more than doubly stiff. On flat tops that I built the bracing is MUCH lighter than on larger guitars.
A tall arch, all other things being equal, will produce a stiffer top. I notice that your top seems to have about 3/4" arch, much as I would expect from a 17" or even 18" archtop. Is is also equally thick? Mandolins have roughly 3/8" arch, for comparison. It may be too late now, but if you do give it a second shot you might try a lower arch. In the interim, you might consider thinning the recurve and see if that gives you a better tone.
I've not built a small archtop yet, so take my suggestions with a grain of salt
