Oh I entirely agree that it's possible for stagnation to happen, but with all the technologies and information that Voyager brought back from the DQ (not the future ones), I would argue that the Feds would have a field day when it comes to R&D for the next several decades which will affect their techs for a century or two ... and they are bound to develop their technology further and further.
If TNG is to be taken into account then the Feds would start implementing Temporal based technologies into their systems by the 26the century (at the latest).
I don't really think the Federation can afford a stagnation period past 24th century.
If there's anything we learned from TNG and DS9, is that the Borg initial encounters with the Feds gave them ample amount of time to prepare prior to the DW, and all they did were 'minor blips'.
In reality such blunders wouldn't have happened ... which is why I give 'credit' in regards to those blunders to the writers who wanted to increase the drama.
But let's not go into that debate again.
The firepower in the Trek universe would definitely saw increase.
I mean ... we have an actual example of the NX-01 and multiple amounts of Archers era ships having virtually no effect on the 1701 shields.
Granted, we don't know just how powerful the 1701-A would be against the 1701-D, but I would say that the differences in technology, computer response times and over all power output generated by the weapons/shields of mid 24th century would produce a close effect like the Defiant in the mirror universe (Archer's era) did.
In any case, one of the main reasons why Betazed fell was because it's defensive systems were 78 years out of date.
That much has been stated, and I would argue that it's quite probable how the firepower between an orbiting weapons platform of Kirk's era and a new 24th century era one is quite big.
It has to be if you want to compensate for 100 years of shields and weapons enhancements that happened.
The best the R&D made was NOT the Galaxy class.
The only reason why people glorify it is because such a big deal was made out of it, the TM explains it in detail and essentially it was the point in Trek when we began seeing new designs inherent to that era instead of the old ones (which were still used a lot), when in comparison to the Sovereign class (I think you mentioned yourself at one point) the Galaxy is less advanced/stronger.
I kept hearing of people how they say the Enterprise D was 'huge' ... when in fact it was twice as small in comparison to the Romulan Warbird (albeit almost evenly matched).
For the sake of the story and drama, you will never see 4 Galaxy class ships against a Borg cube.
Well, not on a Trek TV show.
And for that matter, even if it was 8 Sovereigns that fired all at once with all their weapons, the writers would come up with some kind of an excuse that would nullify the effect so the Borg could live until the hero ship arrives and blasts it to pieces with the final blow.
Makes the rest of the Fleet look like idiots.
