it's not cast, it's forged...and when my guy did it it wasn't "butt-welded", either.
I personally have no doubts about the strength and reliability of a Tig-weld-repaired DO if it's done right, and that's a big IF. I also trust my frame repairman, and if he had told me that mine needed to be removed and a new DO brazed in place, I'd have taken that advice. He certainly can braze every bit as well as Tig weld, and he would have charged me more, I'm sure, so it wasn't done for his enrichment.
BTW, mine was a cracked Campy 1010B, another short forged dropout that is very prone to cracking...it's not just a SunTour (or Tange) malady.