For comparison with Horizon, here's a list of Federation (not just Starfleet) shipyard worlds, by combined berth size and number of berths. (I'm only including berths that have been completed).
1) Mars - 22mt across 11 berths
2) Earth - 13.2mt across 7 berths
3) Amarkia - 12.5mt across 8 berths* (5mt across 5 berths are auxiliary)
4) Vulcan - 10mt across 6 berths
5) Andoria - 9mt across 6 berths
6) Apinae - 8.9mt across 7 berths
7) Gaen - 7mt across 5 berths
8) Tellar - 6.5mt across 5 berths
9) Alukk - 5.8mt across 6 berths
10) Ferasa - 5.5mt across 6 berths
11) Rigel - 5.5mt across 3 berths
12) Indoria - 5mt across 4 berths* - no berths greater than 1.5mt
13) Betazed - 4.8mt across 6 berths* - no berths >1mt
Various other worlds, none with more than 3 berths or more than 3.2mt combined berth size