You're missing that the five numbered NR Fleets were not the only warships the NR had access to. Thousands of singular systems, and interstellar confederations, that were part of the NR had home defense fleets, ranging from a rickety corvette or two to places like Mon Calamari or the Hapes Cluster that had dozens to hundreds (or more) large capital ships. These forces could be added to the official NR fleet command if needed. They are how order was maintained in the galaxy without the Coruscant-centered government having 25,000 ISDs like the Empire had at its height. The Empire took control of the home defense fleets right after its establishment and disbanded them or folded them into the Imperial Navy. They came back into existence with the NR. Fleets like the Dornian Navy (~80 capital ships iirc). The things you say bear no relation to any canon except the one in your head
Local fleets are not purely New Republic fleets. Those are local sector fleets that can jump to either side, and they vary greatly in size and strength. All it takes is for the Empire, the Vong, or some other third party like the Confederacy from Legacy of the Force, to approach their rulers with a decent offer, and BAM! They're against the New Republic/Galactic Alliance. I mean, that was pretty much the plot of LOTF.
The Old Republic learned this the hard way. Most of their fleets prior to the Clone Wars were ALSO local sector defense fleets. Their national navy was even smaller than the New Republic's. Then the Separatists showed up on the scene, and many of these local defense fleets started joining the Separatist Navy. Hence why people agreed with Palpatine when he started building up a unified navy during and after the Clone Wars.
These local defense fleets are like the Ailon Nova Guard. They fought for the Empire during the reign of Palpatine, fought against the Empire after the Battle of Endor, then when the Vong showed up, they fought for the Vong.
Also, I'm pretty sure Mon Cala's fleet is one of the five NR fleets. Mon Cala is their biggest and most loyal shipyard world. Shit, their navy practically IS the backbone of the NR's navy at this point.
This "local fleet" defense is rather pathetic. I mean, it canonically proved bad for the New Republic and the Galactic Alliance. These local fleets outside of the Hapans were all but the north side of useless during the Yuuzhan Vong invasion. More than a few of these local fleets betrayed the Galactic Alliance for Thrackan Sal-Solo's Confederacy, while ironically, the Empire stayed loyal to the Alliance. And need we be reminded of how useful they where when, during the Legacy Era, the Empire invaded again, and reduced the Galactic Alliance into a rump state that'd make the Imperial Remnant look like a king's domain?
You can glaze the New Republic/Galactic Alliance all you want. Canonically, the Empire crushed them and had the last laugh. And what was left of them needed the help of one half of the Empire to defeat the other.
XD
The Imperial Remnant had 3x-4x the territory in 13ABY than it had in 18ABY, which begs the question of how it managed to lose 65-75% of its territory to the New Republic, losing two major campaigns (in 14 and 17ABY), in that time if it had a larger military force.
Mostly because of the chaos caused by infighting and the Dark Empire campaign being lost? I mean, they had fucking Coruscant then lost it again, so they had to retreat back to friendly territory.
In the second campaign in 17ABY the Remnant even allied with Daala's independent Deep Core Imperial forces which should have given it an even bigger edge over the New Republic, Daala still got decimated by Bel Iblis' Fourth Fleet and then Pellaeon's forces were badly beaten in five separate engagements in a row by the combined units of the Third, Fourth, and Fifth New Republic Fleets.
That's one campaign. And they had to combine the efforts of several fleets, as well as an outside element that sat out the most important battles of the GCW. The Empire by that time is far smaller and weaker than what it was, and it took more than half of the New Republic fleets AND an outside element to defeat them. Even though by this time, the NR was way more than twice the size of the Empire. It goes to show that even a quack like Daala could be a threat.
It's canon that the entire Imperial Remnant fleet ISD-class and larger at the start of NJO was about 200 ISDs and 1 SSD
I just said that in my previous post. Also, most Imperial ships are not ISDs. Even during the Empire's height, ISDs were saved only for important missions.