Without breaking your spoiler tag too much:
Even assuming the Kelvin was destroyed by weapons built in the future, it doesn't necessarily follow that the data gleaned from the Kelvin's "black box" will provide enough information for Starfleet engineers to understand the technology behind those weapons, let alone lead to Starfleet engineers devising countermeasures. It further then does not follow that a Constitution class ship would need a configuration which deviates from the original in order to incorporate those countermeasures. Some will argue -- as many have -- that the configuration of the new ship is no different from the configuration of the original, i.e. saucer, neck, secondary hull, pylons, nacelles. Up to a point, that's true. But as I've also argued, all iterations of the Enterprise (barring NX-01) have that configuration, and that doesn't make the designs identical. The 1701 we're seeing in this film is not a Constitution class design. Okay, not the design originally referred to as Constitution-class. (Ha! Headed you off at the pass! Yeah, you in the back! You were about to say "It's Constitution-class if they say it is!" Weren't you? Yeah, I got your number! :P )
"Now I did a job -- and got nothin' but trouble since I did it, not to mention more than a few unkind words as regard to my character, so let me make this abundantly clear: I do the job... and then I get paid. Go run your little world."