Given that Horween offers many different hides, and there are several different Italian tanneries, all of which offer different hides, any comparison is necessarily a generalization. That said, Horween's standard FQHH is very rigid and stiff -- it wears like a suit of armor. Moreover, in my experience, Horween FQHH is often rather flat and lacking in grain/character. In contrast, the Italian horsehides I have seen are considerably less rigid, more pliable, and have more grain/character. Of course, everything is relative and, as MP noted above, Lamb is much more pliable than Italian HH.
If you are riding a motorcycle and need a bullet proof jacket that can protect you during a fall, Horween FQHH is a good option. If you do not need this level of durability/protection, I personally find Horween's FQHH unwearable -- the leather wears you and overly constricts your movements -- it is work to wear (as opposed to work wear). Some say that, over time. Horween FQHH breaks down and becomes much more pliable. Some say any meaningful change in pliability takes many years of regular wear.
Below is my Aero FQHH Highwayman. If that leather had any more character, it'd be played by Robert Downey Jr.
And Chrisgold is correct, the leather is only stiff for a few months. Do you mind providing some examples of leather that you consider to be interesting?
Your jacket is spectacular and has tons of character. That said, the jacket depicted in the photo appears to be well worn. My comment was in reference to new Horween FQHH, as distinct from well worn FQHH.
Regarding break-in, I am pleased to hear that your jacket only took a few months to soften and become more pliable. On the other hand, I have read many accounts from Horween owners of jackets remaining stiff after many years. Moreover, given that I live in a warm climate with fewer opportunities to wear leather, it takes longer to break in a jacket (particularly if it is part of a rotation of jackets). The Horween FQHH fit jacket that I received from Thurston Bros was ridiculously rigid and, IMHO, completely unwearable. I would never suffer through the effort required to break in that jacket.
The following are photos of NEW Aero Jackets made from Horween FQHH (not tumbled or Jerky):
IMHO, these leathers are rather flat and lacking in grain. In contrast, the following are photos of jackets made from Italian HHs (since that was the original posters point of comparison):
IMHO, the new Italian HH has considerably more grain and character, as compared to the new Horween FQHH. Of course, that is an obvious generalization and there are countless exceptions. Likewise, whereas I selected photos consistent with my premise, one could no doubt find photos that suggest otherwise. Moreover, there are many variables that skew the analysis in one direction or another, including variations in the raw hide before tanning (not all horse hides are the same), whether the hide was corrected, variations in the tanning process, manufacturer specifications, etc.
Your jacket is fantastic! That is all that matters.