I know what you mean LT, it doesn't make sense given that the pasteurization process is much higher temp.. but it seems to do the trick for LOs who are outgrowing their MPI already... full blown MPI - it won't make any difference.
When he was younger I did a dairy free diet and it helped probably 95 percent with the eczema but I never was able to totally get rid of the mucusy poos.
Lactose intolerance doesn't generally cause eczema or mucous - both are MPI/MSPI symptoms. Did you do a complete dairy/soy elimination including hidden sources? Things like bread etc almost always contain dairy and/or soy... If you didn't do a 100% elimination, the trace bits you got from hidden sources would have been causing the mucous and bit of eczema that remained.
Now that he is over a year old, he will start to outgrow the MPI/MSPI fairly quickly in phases... you will see he is fine with things like yogurt/cheese (the proteins aren't as strong as they are in cow's milk)... and then over time, he will be fine with more and more cow's milk as well. My DD is sensitive to casein specifically, and she was unable to have even 3 ozs at a year of age without waking screaming from naps and having cryouts all night... now, at 2.5yrs, she can have a 4 oz serving every couple of days without too much trouble..