You don't understand SATA, SSDs, latency, and protocols if you believe this. Its so easy to look at published bulk data rates and jump to that conclusion. USB3 is a wild west full of too quick to market not fully tested incompatible stuff, and a few good efforts. USB storage protocols layers are a bandaid at best and has been proven to be troublesome and slow in the real world for anything other than perhaps backup destinations or portable storage. Running your OS off a USB device day to day is a disaster waiting to happen. Those of us that need a mobile boot device have several to use as backups.
My Mac has been so much happier now that I disconnected all the USB storage devices and went 100% TB. Now for perhaps the consumer with low storage performance demands, you could say USB may be adequate, certainly not better. Life is full of compromise, however.