How close is the published The Silmarillion to JRRT's Silmarillion?

[Galin]

Aside from making a mockery of the name Ereinion (how could he be a "scion of kings" when his ancestors had never held the kingship in Middle-earth?)...

Orodreth/Arothir was still King of Nargothrond however, and in the Ereinion text Tolkien notes his descent from Finwe. Plus, I think the only text with Ereinion in it [unless I've missed another reference] dates rather late, 1968 or later, after Tolkien had at least made the change of Orodreth/Arothir being the son of Angrod, and Gil-galad being the son of Arothir.

So a name meaning 'Scion of Kings' seems to have been invented after the switch to Gil-galad [again] becoming a Finarfinian.