I think usb 3.0 itself is just garbage...
Nope, USB 3 itself is fine, but alot of case mfgr's cheap out on the front panel connectors and cables they use, which causes the problems you mentioned and sometimes moar...
I've had a few cases that had 2x USB-3 ports on the front I/O panels, and always had problems using both ports at the same time, even though each one worked fine when the other was not being used. So after confirming that the
mobo header was working correctly, I replaced those el-cheapo case cables with good high-quality ones and whah-lah, no moar issues