It is not a question of which is the lesser evil. Both commercial fishing and farming are threats. Salmon farms are poised to be a huge threat to native stocks. Steelhead could be specifically hit hard. In rivers where steelhead are already in decline the added competition for spawning grounds and food sources could be the “straw that breaks the camel’s back”. Atlantic salmon are more aggressive as adults and the smolt mature faster. These two characteristics alone could spell doom for native steelhead and salmon.
You are correct that salmon farms have hurt the commercial fishing industry. The commercials led the fight to ban farming in Alaska and they may lead the fight down here to regulate Aquaculture. The farms were not stopped up north for ecological reasons or to protect native fish. They were banned to protect commercial fishing.