>> It definitely is in the reference manual and probably also in the data sheet

> I'd didn't see that diagram anywhere else.

Block diagrams alone aren't proper technical documentation anyway. Such things have to be (and surely are) properly documented in text form in the reference manual (and data sheet probably).
Funnily, that P1022 SoC diagram is shown on the P1022DS board product page as board diagram. The real P1022DS board diagram is missing (that's why I linked it from another source above).

> He seemed to think that some users would find the system more appropriate
> for something like an R5 240.

I read this comment he made regarding the use of GCN4/Polaris cards with A1222/Tabor:

"Polaris cards cover the full range from low to high-end, just like their predecessors."
https://keasigmadelta.com/blog/amigaos-graphics-survey-2018-rise-of-the-emulators/