My late father in law was a master pipefitter and quite outspoken and set in his ways. He would only use black iron pipe and fittings whenever possible. He said that plastic stuff is junk. I would tell him that science says "plastic" pipe for drain or venting applications is better.+1 for cutting out the old work and replacing with new soldered copper.
Why are there so many people so adamant about copper vs PEX? Doesn't PEX meet all the technical requirements for house applications. Are all those fans of copper too set in their ways?