USB 1.1 Full Speed is 12 Mbit, i.e. 1.5 MB/s theoretical, zero overhead accounted for. That's an order of magnitude you're missing there. Whether it matters depends on how large the drive is, I guess.

It also bears pointing out these microcontrollers have built-in parallel memory interface buses, which are likely compatible with IDE (which is just ISA == the 8088/8086 parallel bus on a cable.) With DMA, ketchup and fries…