If this is true - and I'm unaware of any canon that specifically denies it - what would it mean for the universe?
I would certainly agree that no canon
specifically denies it, but there are good reasons to think it's not true:
1) WarShips (including many of those listed in the various TROs) were in production from 2300 to 2571, during which period the Hegemony and its neighbors were at least notionally hostile towards one another. We know there were many naval actions during this period (the Capellan attack on Terra Firma in 2409, for example; the
Bonaventure entry references a "powerful Kurita destroyer squadron" raiding Imbros III at the start of the Age of War.) If the Houses weren't relying on native production, where were they getting their ships to prosecute this conflict?
2) At least two of the House vessels we've seen -- the
Davion and the
Du Shi Wang -- predate the Star League, yet continued in service until they were all destroyed in the Succession Wars. If the Houses had an expectation of acquiring hand-me-down TH/SL ships, why keep these old vessels in service? And if "national pride" is your answer:
3) TRO3075 makes it clear that as soon as the Houses got their hands on BattleMech technology, they started designing their own versions so as not to be dependent on the Hegemony-designed
Mackie. It would be surprising to discover they felt so strongly about BattleMechs, but not about the vessels that could break a BattleMech battalion with a single shot.
4) Finally, as a matter of textual analysis, this prospect seems to be obviated by the fluff of a lot of the ship classes. We specifically know for a few classes (
Aegis,
Baron,
Vigilant) that they were sold or gifted to the Houses. Other classes seem from the fluff to be confirmably out of service by the beginning of the Amaris Crisis (
Dart,
Farragut [4A]). Then there's another subset for which the fluff seems to account for all possible vessels in the class by establishing that there were X number of surviving vessels at the end of the Amaris Coup, all of which accompanied the Exodus fleet (except, in some cases, for Y that were scuttled) (
Texas,
Avatar,
Sovietskii Soyuz [4B],
McKenna,
Black Lion [4C],
Riga-that-became-
York.) This leaves several classes, such as the
Carson or the original
Riga, for which the last vessels were withdrawn from service or mothballed and
could have been sold, or for which we have no information regarding their fates (
Congress). Point is, that's still pretty slim pickings in terms of a breadth of classes, particularly if you assume that the standard vessel of each class in the Star League fleet wasn't going to be sold off on the eve of the Succession Wars (your
Vincents,
Essexes, etc. [4D])
[4A] Of course, this might be looked on with some suspicion, since apparently the Wobblies managed to scrounge a
Farra from somewhere.
[4B] Same for a
Sov.
[4C] Though again, we know the FWL was able to recover a derelict, and the Wobblies have two (assuming
Xanthos was not renamed after being subverted.)
[4D] Though who knows? Despite being the only troop cruiser that we know of in the Star League arsenal, many
Potemkins were decommissioned after the liberation of Terra and at least some were dismantled, but at least one (LCS
Nightwind made its way into the Lyran navy.
With that diatribe out of the way, in response to your question -- I don't think it'd change things much. One would imagine that the lack of infrastructure to build WarShips would help explain why they vanished so quickly in the Succession Wars, though, even though presumably some of your shipyards are going to be deep in the heart of the nation in supposedly safe places like Tharkad and Atreus.
