How many nuclear-powered naval vessels did the U.S. provide to Japan? Or the Philippines? Or Guam? Or Puerto Rico? How would the U.S. Government have responded to a demand from one of their governments for that kind of technology?
To be sure, Japan had no technology gap with the US (except perhaps in the construction of quality steam turbines). OTOH, Guam or Puerto Rico had no industrial capabilities or industrial, military or political aspirations. So to run with this already stretched analogy where the entire planet has to consist of islands, we'd need an island nation more akin to the Native America at the first arrival of the Europeans. Does one provide the technology for ocean sailing (almost replicable by the level of "industry" Native America possessed, with a little bit of expert advice on a plethora of details and a few grand lines) or not? We know the historical answer, but if the Europeans had been Vulcans, and the Native Americans had possessed the ambitions of the Earthlings...
It is rather futile to play games on "what would the US have done", alas, because by the time there
was a US, the world had lost its supply of underdogs with industrial potential. One might switch the focus a bit and argue that Japan was
almost like such an underdog before Perry, and that the European powers did provide Japan with parity technology comparable to NX-01, while at times attempting Vulcan-style "moral restraint" for various largely political goals. Or one might go to Africa of the same time period, and indeed see definite underdog nations being armed and equipped - but there the lack of indigenous industrial potential affects the analogy.
I wouldn't be surprised if humans and Klingons both patronized the same pan-galactic defense contractor during the 22nd century (the El Aurians, maybe?) and that photon(ic) torpedoes have always been the staple product of some enigmatic but fanatically neutral alpha quadrant race.
Certainly the parity weapons of Earth emerged suspiciously simultaneously with their first true deep space power projection mission, too early to be the result of that mission. One would then suspect there had been some deals behind the backs of the Vulcans, yes. And in ENT, don't we actually see Earth operate a few ship types that are later established to be in use by other local powers? The odds of those aliens buying Earthling stuff are pretty slim, but the odds for the opposite happening sound reasonable. After all, we can always sell them local booze; luxury items and beverages or quaint rustic stuff seem to cut it as hard currency even in the TOS and TNG eras.
The only thing we know for sure is that Starfleet didn't get that technology from the Vulcans, though it's very likely that Starfleet phaser weapons at the time were still inferior to Vulcan weapons.
One might argue T'Pol was being disingenious when indicating ignorance of photonic armaments in "Sleeping Dogs", as those might have been her explicit orders... "They'll run into all this eventually, but you are to stall; they are not ready, or at least we don't want them to be."
OTOH, I'd love to interpret the early Earthling antimatter torps, the "photonic" ones, as corresponding to the TNG TM description of crude warheads where macroscopic lumps of matter and antimatter collide. This technology might have reached its pinnacle in the TOS era, in the form of massively powerful versions of the crude devices - but that tech would have had its tactical limitations, and the suggested more efficient mixing system would indeed emerge for the TOS movie era, allowing for the close-up action, precision strikes and efficient kills or woundings we see in those movies. The big bang warhead might still persist as an alternative, just like USN kept a few wire-guided fission torpedoes in stock even when conventional ones reached the level needed for assured kills of successfully intercepted Russkie boomers.
Timo Saloniemi