External SSD for MacbookPro - get the right speed?
The external USB3 ports on the MacBook Pro Mid 2014 are definitely capable of 5 Gbps, and so it it is indeed meaningful to connect a SSD that way.
Note that the actual speed of the USB links changes depending on what you connect to it. So if you connect some older, slower device - such as a for example an old USB mouse - you would see the speed listed as being significantly slower. The same can happen if you connect an older USB hub, or you connect several devices to the same port of differing speeds.
Also note that the MacBook Pro has internal USBs for things like the keyboard, trackpad and camera. The speed of these is irrelevant in terms of the performance you'll see with externally connected devices.