"graphics memory" is probably not the right term here. While the Pro SSG does have 2TB of storage on board, that comes in the form of a NAND flash, PCIe SSD (from Samsung IIRC). While fast, this SSD provides single digit GB/s bandwidth at most, compared to the hundreds of GB/s of bandwidth that the DRAM-based GDDR5 or HBM provide. When we say "graphics memory," we're almost always referring to the latter, and never see more than maybe 32 GB of DRAM based memory on board.
Yeah, that seems like false advertising. I believe that much true HBM/GDDR5 would have to cost tens of thousands of dollars. So I was skeptical. That said: if I could get a card with that much real GDDR5 on it, I'd consider paying whatever it took.
GPUs are generally not latency optimized anyway - if an app is sensitive to tens of microseconds then it belongs on the CPU, broadly speaking.
AMD's advantage here is getting drop-in throughput, by switching the SSD directly to the GPU. Thus, the onboard SSD doesn't waste host PCIe lanes (4 lanes, typically) that are getting hard to come by in regular desktop computing systems.
