Beauty is in the eye of the beholder. I see beauty not only as physical traits but as the effectiveness in its duties. That is in fact a beautiful 15" gun, perhaps one of the best of them. However, nothing of that time will match the raw damage and range that can be provided by a 46cm/45. The elevation angles are nice as well, but there is nothing in those guns as physically appealing as the Yamato's 18.1" rifles. Their taper is bland and straight, their breech unique but geometrically bland, and the loading system is unnecessarily complicated with two separate lifts for the same package (more effeciency with Yamato's specialized loading and safer separation of powder and shells in magazine), and the halving of powder loading saves space but wastes time. The ability to load all 6 bags at once could shave a full second off your loading time.
In all, I cannot in good conscience find your 15" Italian guns more beautiful. Besides, do I have to repost the Canada song to reiterate that sometimes bigger is, in fact, better?
I must acknowledge that damage cannot be matched, but the range can absolutely be matched by the gun I've pointed to; at an elevation of 45°, the 40 cm/45 Type 94 could throw its AP shell at a distance of 42'030 m, while at an elevation of 36° the Model 1934 could hurl hers at the distance of 42'800 m.
As you said, beauty is in the eye of the beholder, so you are entitled to find the geometries bland.
I cannot comment on the technical details, since it seems that you are more knowledgeable about them than I am. However, a resource I use fairly often, the website NavWeaps.com, and in the page of the gun it is mentioned the report of the USN Technical Mission to Japan, that talks about "an unduly large factor of safety had been allowed in the design of the turret machinery as a whole, resulting in a very heavy mount, the total revolving weight of one turret being 2,510 metric tons".
Also, it says that this gun's construction meant that it was possible to reline it only by boring out the inner A tube, a process so costly and complicated that it was more convenient to outright replace the worn out gun, although the Yamato-class' brief service meant that there was no occasion to do so.
Instead, the Model 1934 has been long criticized for its low barrel life, but for a battleship designed to operate close to home ports this was hardly a disadvantage; in fact, whenever the barrel was worn out it could be replaced in a day's work, easily enough.
Anyway, you asked about "effectiveness in its duties"; while it's clear that the Model 1934's duties were different from those of the Type 94 (which was in another league), for the duties it was supposed to perform (get out of port, pound the heck out of enemy ships, then get back home) it would have been by all means adequate. What really bugged this gun was the wide tolerance admitted for the weight of shells and especially the propellant bags, which often resulted in a far too high dispersion. In the few instances in which more even batches were available, these guns shot well.
So, in absolute terms you are right, bigger is in fact better; but in relative terms, considering how much effort went into the Type 94, and the respective needs of the two navies, it would've been (other than impossible) impractical and a waste for the Regia Marina to build such monstruous weapons for itself, while a more modest (but very respectable) design proved adequate.
It's all relative.