No they aren’t. Raw speed is only one factor. And even then comparable cards are still around $200
You're right, the other factor is how the console accesses the memory through the I/O. That has nothing to do with ssd specs. You can get a ssd with faster speeds than the series x for $150.
If you don't think it cost money to customize a nvme m.2 ssd to be much smaller then I don't know what to tell you.