I actually think the Kelvin is an over/under nacelle ship as per the flip side of this reasoning. Over/under designs, like the Akula class, tend to be more combat oriented ships (at least in fandom). The Kelvin seems to be packing a fair number of gun turrets ahead of the bridge for a surveyor type.
I don't think you can expect the designers for a movie to be aware of any of the conventions established by fan designers. And the only canonical starship class I'm aware of with an "over/under nacelle" design is the Constellation class, such as the Stargazer, which was an explorer.
I'm pretty sure the size of the ships has to be significantly bigger than the originals. The trailer and large bridge size seem to suggest that, anyway. I sure as heck don't think the new bridge could fit in the old ship, it's too wide.
The apparent size of sets in photos can be misleading due to vagaries of design, focal length of the camera lens, etc. For instance, the TNG bridge looked larger and more spacious than the TOS bridge, but the set was actually a little smaller.
The bridge in the released photo looks about the same size as the original bridge to me. I think it looks wider because Kirk's chair is farther back, closer to the aft wall, so the perspective is different, making it look like there's more width between the chair and the turbolift.