To me the issue with RPis storage is the lack of hardware encryption. No matter how much you increase its I/O capabilities it won't be able to use disk encryption without having to rely on CPU cycles.
I'm still surprised that they did not include a crypto accelerator on the Pi4. It seems like a very low cost peripheral, with a high performance impact for many use cases (drive encryption, network encryption, etc...). I ran some benchmarks between a Pi4 and a Nanopi M4 and it wasn't even close.