So . . the Metoreoum is a heavy gunboat then? The KessRith employ slow ships with heavy shielding and armour, it's designed to combat that fighting style is all. Adding 100 tons for an FTL drive (more like 115 since it'll be a new percentage of the overall weight), what's the point? (most Leviathans only have 1000 ton bays, adding any weight to the Meteorum will mean that most can't carry 'em). Renegade Legion FTL drives aren't for intrasystem travel. Ships use FTL to travel system to system and then move via normal space therein. It's not like freespace where ships launch from a carrier, jump to some other place in the system, and then do their thing, and jump back.
If you don't like the Meteorum as is, then leave it on the KessRith front. It's that simple.
It's not an exaggeration to carry an Escort on a Leviathan, it's just pointless. If an Escort is self-contained, and perfectly capable of flying around on its own, why build another larger ship to carry it? There's no reason for it.
As I said before, only 5 ships can carry anything bigger than 1000 tons. And again, what's the point of it? Why carry a corvette like the Pharetra with 6 fighters when your ship already has 200 fighters in it? Why carry a Cingulum when the Cingulum has an FTL drive to accompany the ship on its own? I think you're confusing Leviathans with Star Destroyers. Star Destroyers are big ships with a bunch of fighters, and a bunch of ground troops, and a bunch of "pre-fab" bases and a bunch of everything a person would need or something like that, according to the Fluff. Basically they do everything that's needed, a little unrealistic. But Leviathans aren't. They're just warships which do the job of destroying other warships. Similarly, Corvettes like the Cingulum are for patrolling areas than are not important enough to warrant a warship, Corvettes like the Pharetra are for bringing a few fighters to some backwater system to mount a quick raid. If you make some jack of all trade ships you've ended up with something that can do nothing well. If you're carrying tanks or troops, you need bays for those ships and you need living quarters for the crews of those transports. But your ship isn't always going to be involved in planetary invasions. When you're not you've suddenly got a lot of space spent on transporting people and materials when you could be carrying more weapons instead.
And yeah, a Leviathan even for a short time could carry a few more tanks or whatever. But really, if a Transport is like a Carrier, then most transports are going to carry what 100-200 or more tanks? Now if you've got 5 transports with a thousand tanks would you rather load your Leviathan with a few transports, to carry 30 more tanks? Or would you rather load it up with some heavy gunboats, to ensure that the transports can do their jobs?
Harpy's a possibility but would have to look at the naming conventions, TOG doesn't seem to use much in the way of mythology for their ship names from what I can tell. But could be wrong. (where the Commonwealth has the Pegasus, etcetera). Though if you model the ship you can name it whatever you like.