That's how starved Vega is for bandwidth. Remember, Vega 64 and Fury X have the same bandwidth. Vega 64's shaders can handle about 80% more throughput per shader than Fury X thanks to NCU and higher clockspeeds but it only gets a fraction of that because Vega 64's shaders are constantly waiting on the memory subsystem to feed it more data. Evidencing this is how miners underclock and undervolt the GPU while overclocking the VRAM. Vega 20 finally gives Vega the bandwidth it has always needed. Granted, if the task at hand doesn't require lots of higher level memory accesses, it won't see much benefit from the extra stacks.