That is PCIe 3.0. For example the Samsung PCIe 4.0 990 PRO just released: sequential read 7.45GB/s and write 6.9GB/s — https://arstechnica.com/gadgets/2022/08/samsung-announces-99...
2. Can confirm these writing speeds
a consumer SSD will have about 50k iops at that 300-500megabyte/s . The access pattern will not practically matter at all until you saturate that or get close. The drive is effectively constant time until you hit the limits of the interface, or at least get somewhere near it. A consumer will never get near it.
So they can expect, and consistent testing shows, they will get 300-500 megabytes/s in real world conditions, and even harsh conditions.
I actually have no idea why you don't just say "yeah, i was wrong" and move on. It's clear you are wrong about this - there is no data to support what you are saying. It's also totally and completely orthogonal to a more rasonable argument - they don't care about the speed anyway.
IE arguing they don't have equipment that can saturate 1gbps is silly - they clearly do. arguing they wouldn't care either way because the speed difference doesn't matter to them is more reasonable.
