Some (which ones I do not know) of STI Frames/Slides are in fact made by Armscor (Philippines). Same company that makes Rock Island. So, not all STI's are "truly" made in TX.
STI's are put together in Texas. And they are nice guns. But are they worth double the price of a Rock Island? Probably yes to many, but probably NOT to someone looking for a good, budget 1911 that has a very good C/S policy (if needed).
I do not own a Rock Island or a STI. I have never seen a STI, other than pictures.
I have held and examined a Rock Island but never shot one. I have seen that the quality, fit & finish and C/S make their pistols a good value for the money.