Seems like the Ent-D being twice the size of the original Enterprise is something that was written once, early on, in the series bible.... and then immediately forgotten
as production began on the actual series. Lol
I mean, was there ever any shot that showed the ship being much larger than other established ships? I can't think of one. Even the Bozeman/Reliant from Cause and Effect was twice as big as it should be.
Seems like the only time they got the scale right was with the Excelsior model, but that was probably just by accident.