I grant all your points, man. In my opinion, these combine into a probability that the Constitution was the most advanced and most powerful Federation vessel, but in the absence of any definite evidence, however, it remains an unproven opinion.
As for the Kelvin, however, I'd like to remind you that the timeline had already been altered in First Contact. There's no way to know exactly what the consequences of that are, but personally I've always thought it explains the "differences" in Enterprise.
It has never been explicitly stated that the events in First Contact actually changed anything even after Cochrane gives the Vulcans a shock at the end of the film, even so it would fit in quite well with the new ship sizes and uprated technology in the new films.
It was suggested years ago that the First Contact film was the trigger for the Mirror Universe alternate reality but I never really bought into that as it didnt flow very well.
There have been so many time incursions that I am amazed the changes in the new films are as "shallow" as they are tbh, same people, same place etc etc.
I think the writers have got the mix of old and new about right.