I know I might be opening a potential can of worms but how should we settle on ship sizes?
We have actual treaties limiting them so I believe there are some sorts of standards the entire galaxy agrees on to classify them. I am partially ask this since one of the White Corps' military shtick is to skirt around these rules and field ships that might appear to be in a certain class but in effect they are more powerful.

Since without an opening argument this would take an eternity here's my potential list on starship sizes, using the largest dimension (usually length) to measure:

[b]Hyperdreads:[/b]>5000m
[b]Dreadnoughts:[/b]2000-5000m
[b]Battleships:[/b]1000-2000m
[b]Battlecruisers:[/b]700-2000m
[b]Cruisers:[/b]450-1000m
[b]Destroyers:[/b]200-500m
[b]Frigates:[/b]100-300m
[b]Corvettes:[/b]30-150m
[b]Heavy Strike Craft:[/b]15-40m
[b]Starfighters:[/b]<24m

This is merely a suggestion of mine and mostly used for standardish shape ships. For example if you have spherical or flying saucer shaped vessels this number might get lower to compensate. It depends on you, of course. Furthermore as you can see I included a fair bit of size variance so people have decent freedom to pick what they feel the best. Overlaps are also a thing since reasonably thinking the heaviest destroyer and the lightest cruiser shouldn't be that far apart (and might even be switched as far as relative powers concerned). Battlecruisers have almost the same size limits as battleships because historically BCs are basically BBs with lighter loads and different roles. The difference between a BC and BB is more in terms of tonnage and armor/weaponry than anything else. Lastly I split "strike craft" category in two to account for gunships/bombers that are less maneuverable and the true starfighters. This way it's even less likely one would have "starfighter corvettes" which the GM was apparently fearing.
That being said this is just a list of values I put together in like 10 minutes.
Feel free to criticize it. :lol

EDIT: I am also not claiming that the treaty only limits the size of vessels. If anything that's just the start. As the GM implied with the description of capital ships there's a fair amount of minmaxing going on with Detente era warships so likely the power generation/consumption is another key element they limit. But I leave that to you, the size chart above is only there for [b]aesthetic[/b] purposes. So we don't get things like 500m long hyperdreads while the other side has kilometer long corvettes.

EDIT2: Spellchecker trolled me (see the last bold) so I went to fix that.