I always saw the (initial) Khitomer Accords as being a cease-fire agreement that allowed the Klingons to rebuild both Qo'noS and their overall economy following the Praxis Disaster. By the 2340s, the Klingons achieved this and hostilities with the Federation eventually resumed sometime later, escalating in time to a protracted war.
In this war, the Federation could have been weakened over time by a sizeable number of war-weary member worlds deciding to secede and perhaps sign non-aggression pacts with the Klingons and/or by the destruction of many key production facilities, losing a great deal of its war machine infrastructure.
Nob Akimoto wrote:
Although referred to as a "warship", the Enterprise-D still looks quite similar to the one in the "proper" timeline. Although she has a substantially different bridge module, the basic structure of the ship is the same. This suggests the war started while the Galaxy-class design project was pretty far along, perhaps not as long as the "20 years of war" figure bandied about in the episode.
If we go by ye old TNG Tech Manual
, the Galaxy Class Development Project was already underway by 2343 (supposedly a year prior to Narendra III according to Okuda's chronology). But the conflict between the Federation and the Klingons could have driven the design's mission from originally being a multipurpose exploration ship to it now being a troop transport, intended primarily to carry thousands of combat personnel to wherever they were needed.
Enterprise-D] was the first Galaxy Class warship built by the Federation. Forty two decks. Capable of transporting over six thousand troops."
--Lieutenant Tasha Yar
It seems to suggest that in this timeline, the USS Galaxy
was renamed USS Enterprise
-D during her construction, but her design retained the name Galaxy-class.
In any event, I think the Galaxy-class was always meant to have "battleship-grade" capabilities, and that the war with the Klingons merely called for the reduction of resources (personnel & onboard facilities) dedicated solely for scientific research and the total elimination of spouses and children (the presence of Guinan, however, tends to suggest that at least a very limited number of civilians could still serve aboard fleet vessels in a support capacity, perhaps at a captain's discretion).