I think this is overlooking two of the most important benefits of multi chip modules, re-using engineering and simpler supply chains. Once AMD has designed their eight core die they've got a design they can re-use between the cheapest desktop CPU without integrated graphics and the highest end server part. And, modulo binning, you can reallocate your dies between market segments as demand dictates. You've still got different IO dies for different segments but those on are easier to design and on less in-demand processes nodes.