I disagree with this statement. The Delos can sound quite disagreeable without proper loading, at least in my system using SUTs. If you pay attention to transients and timbre you get important differences depending on loading. If you aren't tuned in to acoustic instruments (e.g. good classical recordings) you may not notice this as much.
I disagree with myself, to some extent. It seems that the reason for the large differences that I was hearing was that I was overloading the MM input. So by loading down the Delos I was actually reducing the output and therefore curing the overloading. Had I been using a 8x or a 10x transformer, I don't think that the sonic differences with cartridge loading (above 50 ohms) would be nearly as significant.