In re the three cores for FFG....
when one actually looks into the content of the non-core mechanical material, the overlap is well under 50%.
That includes the opponents, the vehicles, the weapons, the creatures, and the races.
The classes have zero overlap, but the specialties have around 1/3 overlap between Edge and Age. (Class gives some starting skills, and in the case of the F&D ones, gives a rank of Force, with that rank's commensurate white die on force checks. Note that no additional classes are added in splatbooks prior to spring 2019). Now, the force powers in Age and Edge cores only have 30% overlap with each other, but those 5 are 5 of the 11 in the F&D core
The splatbooks do have more overlap... typically one specialty table and 1 of the races is in another line's core or splats. Very few vehicles have overlap, but there are many parallel ships/vehicles in the same roles....
... and a number differ only in trivial ways. The various YT SLF's are all pretty similar.
I will note that during the public beta, a number of us asked for a vehicle scale separate from the ship scale — much as WEG had in WEG 2E — but we were basically ignored. The result? ground vehicles are hard to differentiate.
That is, without a doubt, my biggest gripe with the system. The 20% identical content of the corebooks? I have no issue, because the rest is in fact tailored to the specific subsetting.
And... The Squad rules and the squadron rules work reasonably well. The minion rules are particularly good for the genre. The force rules feel a really good fit to the Clone Wars cartoons, and encompass those and the prequel trilogy, but not so good for the OT - but the choices in Edge and Age, they are subtle enough for most of the OT and its commensurate EU materials.
