I’m resurrecting this post because it hit me again.
I was in the middle of a nightmare situation thinking my pc had begun to kick the bucket, and decided to reformat a usb drive with ventoy on it so that i knew the data wasnt corrupted, and once again hit this slow usb speed issue. I copied over EndeavourOS’s iso file and a few others (archcraft, manjaro, xubuntu, and a couple of necessary boot/repair iso’s) for a collection of about 35GB, and it took about 7 hours to transfer. I actually used the corrupted pc in that forum post initially, but after about an hour thought it would be better to use a more trustworthy machine (a spare laptop I have) based on the circumstances. I went to town and did a few errands and got food, only to come back to see it still transferring.
I’m not sure if i made this clear in the original post (i didn’t reread it since i posted it a while back) but the first few GB’s transfer perfectly fine at the correct speeds. It drops MASSIVELY in speed after that, all the way down to a few hundred kilobytes per second, and the time it takes to complete the entire transfer backs up such speed reports like those listed in KDE’s system tray. It goes up and down at times, but it stays in the 0.5-2MB range, even with usb 3.0 hardware. The most interesting part of this is if you transfer large files, but one at a time (say no more than 1.5GB) they transfer fine and at the correct speed and is easily verified by actually running the iso files or hashing them. The same 35GB of files will transfer in prob about 30-40 minutes depending on how fast you are at copy/pasting the files. It’s not specific to arch either, that transfer was done on a xubuntu install.
The transfer was done with mechanical HDD to usb 3.0 flash drive via a blue 3.0 port, on both computers. Both took hours, and i would’ve done the “small and fast” method but some of those iso files are >5GB.