I haven't had issues with those cable guides, but with new paint, etc., it seems plausible.
I've used teflon tubing where the cable goes under the BB shell (on slightly newer bikes than yours). It does a nice job of allowing the cable to slide without grinding away the paint or anything. The only downside is that rain or spray will wash gunk down into the tube and cause friction. I think that is why the little donut things are installed on the cable in the photo. They cause the water to divert before it gets into the tubing.
Steve in Peoria