Couldn't you supply some real benchmarks?
Like: how long does it (really) take to read the file?
I just tried to read some 200.000 files from an external USB3.0 HDD and it took
10 minutes, 55 seconds
if MP3tag resides on the same external drive
8 minutes, 59 seonds
if MP3tag resides on the internal SSD.
It becomes
6 minutes 43 seconds
if MP3tag resides on an internal SSD and the data also on an internal HDD.
It looks to me like you can expect to read some 20.000 files/minute.