Actually you're right I made one mistake. I forgot that they didn't know Nero was a Romulan until he destroyed Vulcan in 2258; 8 years prior to when the Romulans would reappear in the prime timeline.
Well, they sorta did: it was in Pike's dissertation that the ship from 2233 had been Romulan, and it was implicit in Pike's communication in 2258 that the Feds knew who the Romulans were and assumed that Nero was part of that outfit because he was Romulan. So the big discovery happens at some point between 2233 and 2258, and we don't know quite when and how. But "Balance of Terror" was a Romulan aggression that might have succeeded without leaving a trace or a clue as to the identity of the attackers; perhaps such attacks actually would have been attempted in the early 23rd century in any case, and perhaps a slightly different one backfired?
But the logic still holds in that it changed how the Federation looked at the universe It lived in; And again as admiral Marcus actions show, The Star Fleet of the Kelvin universe was a bit more militaristic than that of the prime timeline.
Or then quite a bit less militaristic, so that Marcus has to concoct a conspiracy to ignite war, and Pike has to draft mavericks to bring some fighting spirit back into the organization.
Reaction to the Narada is not evident in what Starfleet of the 2250s-60s looks like, in that timeline. But we hear it stated out loud that S31 did react. How much of that translated to change in Starfleet? Khan's work is just starting to bear fruit in ST:ID; ships like the Enterprise have apparently been completed without Narada-related input.
Kirk always met giant space monsters that were more than a single starship was able to chew. Meeting the Narada oughtn't to have been all that remarkable and game-changing, either. But perhaps it made Starfleet a tad more cautious, meaning it actually met fewer monsters in the following decades, and in backlash grew not just complacent but bold - leading to early Gorn and Romulan contact. Or then having survived the Narada made them bold outright. Or then searching for the now-missing Narada made them stumble onto the Gorn and the Romulans. Lots of options there that don't involve Starfleet actually upgunning, which is good, because when the Narada does return, they're no more prepared than they were in 2233!
Timo Saloniemi