The TOS episode "Balance of Terror" established that Federation members had no idea that Romulans were an offshoot of Vulcans. The film ST09, which was written after just about everything, showed no surprise on the part of anyone as to the Vulcaness of Romulans, this was set, of course in a timeframe before the events of "Terror". This would at least suggest that there were differences in the two timelines even prior to the Nero incursions.
That doesn't follow at all. We don't hear anyone in the film mention Romulans until the 2258 section, 25 years after Nero's incursion and the timeline split. It's easy enough to assume that someone found out the truth about Romulans sometime between the 2233
Kelvin incident and the events of the film a quarter-century later.
As would also the relative advancement, technically speaking, of both the Kelvin and the JJprise.
Again, that's a difference in artistic interpretation rather than an in-universe difference. The greater advancement is that of the filmmakers who are attempting to approximate the appearance of 23rd-century technology. Obviously the makers of TOS did not intend the
Enterprise to look like it was made with 1960s lights and switches and materials; they just tried to approximate a futuristic technology as best they could with the materials, budget, and resources they had on hand. Modern versions are able to use more advanced techniques and can thus come that much closer to approximating the future technology.
I mean, seriously, do you believe that
The Search for Spock is in a different timeline from
The Wrath of Khan because Saavik has a different face and voice? She looks different, sounds different, acts different, but we suspend disbelief and play along with the pretense that she's the same person. So why can't we do the same when different production designers give us different-looking interpretations of Starfleet technology?
Furthermore, Captain Pike's assessment of Starfleet aside, there does seem to be a more martial aspect to the fleet as depicted in NuTrek and personified by Admiral Paxt..er, Marcus than we were used to for the TOS era. It is arguable that this different attitude was a direct consequence of Earths having been attacked by the Xindi.
It is far more logical -- and obvious -- to assume that Starfleet's greater militarism was a result of Nero's attack on the
Kelvin. I mean, think about it. A gigantic, super-advanced Romulan ship appears out of nowhere on the Klingon border and launches an unprovoked attack on a Starfleet vessel. How do you think Starfleet would react to that? They didn't know the
Narada was from the future, so they'd have every reason to fear that the Romulans had developed new weapons and were preparing for a new war. That's more than sufficient to explain Starfleet's greater militarism.
I mean, the
Kelvin attack was 25 years before the main body of the '09 film. The Xindi attack was 105 years before it. What has a greater impact on current US foreign policy -- the 9/11 al-Qaida attacks or World War One?