The PCI express port looks like it connects to some form of daughterboard for port breakout and is deceiving.

Apple calls motherboards as logic boards making non-apple devices look illogical piles of electronic components. :)

The explanation I got for logic board was from the classic all-in-one Macs. They had a high voltage “analog board” for the CRT, and the low voltage digital “logic board” for the CPU.

IIRC the rationale was a logic board has a soldered CPU, but IBM calls it “System Planar” so yeah

Mac Pros had interchangeable CPUs and Logic Boards IIRC, so as they may as well call it Brainzz however, it won't change the function of the board itself. :)