I'm getting Gen 4 speeds on my Studio, I linked to a MR thread where people are getting speeds well beyond gen 3. I'm not about to beat this horse to death. There is no way you can convince me that I have gen3 like speeds on my M4 when in fact I have verifiable results.
View attachment 2615191
As I wrote, those are pro models. I get the same speeds as you do on my M1 Max Studio.
But I get Gen 3 speeds on my M1 mini and I think lower speeds, in the 2,xxx range on the M1 Air.
The table I showed above shows Gen 3 speeds on base M4 Macs. The M* Pro, M* Max and M* Ultra models have Gen 4 speeds. Though, for some reason, they don't get into the 6,500 - 7,000 range that you can get in the aftermarket NVMe Gen 4 world. It may be that Apple uses lower-power SSDs.