Don't forget in comparing shipyards that not all shipyards are created equal.
You are thinking Galax has the exact same facilities and capacity as those found at Ionus. That's probably a bad assumption.
And BTW "Mass Produced" is a very subjective concept. I'm not sure it's worth really debating. I know it doesn't sound subjective, but it is.
Oh I'm aware, and I'm not making any assumptions.
When I read what Ionus produces I'm inclined to think its the largest shipyard outside of Terra.
But, IIRC, I think Galax already lays claim to that "title" from some sourcebook quote.
Even if I'm remembering that right, the FWL "as a whole" has more total shipyards, developed industry, & overall good economy.
I'm also not trying to debate what "Mass Produced" means really.
I have my own theoretical definition, which basically comes down to some combination of "Major Focus for that Yard &/or the Faction", "Multiple Yards", & "Raw # of ship hulls" in the decade leading up to the Jihad.
As for what makes up each yard, yeah, I don't even try to figure that out.
I recall Galax started out w/ 1 slip for the Fox Prototype & then expanded to like 3 & then set up shop in another system in FS & then moved over to the LC half at Alarion.
In turn Alarion had a single slip for the Fox & after making it they built a 2nd for Foxes & upgraded the first one to Mjolnir construction.
But those are quotes I've read somewhere & I'm not that familiar with the history of Ionus.
As for # of companies & shipyards as a whole, from what I've read most of the "Shipyards" in that system have multiple names & companies that started out as conflicting fluff in the early sourcebooks.
In later books it seems to be pretty common to clarify that the entirety of the Shipyard is partially owned by multiple companies who share the yards.
Like the Shipyards at "Alarion" are named the "Port Simon Naval Shipyards" but often just referred to by the system name, or, might be called the Ioto Galactic Enterprise Shipyards, or the Bowie Industries Shipyards, because both of those companies are part-owners in the "Port Simon Naval Shipyards".
Its odd but it works, I was personally hoping we'd find out there were actually like 3 different locations in the system, hehehe.