The poster may have a far more extensive background with cast bullets than I do. If so, perhaps he can furnish an explanation. I think most of us here are willing to learn, particularly from a knowledgeable source.

In contrast to his statement, I've found that cast bullets that fit well and are of the proper hardness for the velocity/ pressure of the load will perform (penetration, expansion, velocity, and accuracy) at least as well as jacketed bullets.

To get jacketed performance from cast bullets requires some experimentation and benchrest work, but not an undue amount. I think most handloaders have a real interest in this sort of thing. That's hardly being close-minded to better handloads.