Once you’ve installed proper drivers and connected things the device you connected will use a protocol for communication. Some are more openly available for software and hardware manufacturers and others are more tightly controlled.
In the ‘open’ category you mainly have Mackie Control Universal and Mackie HUI. Any controller that supports that protocol will be limited by that protocol. Almost all of the ones you mentioned will use Mackie MCU if I remember correctly. A company like Steinberg could change the assignments so that one input from a controller does something it doesn’t normally do. For example, I think Steinberg could route the fader control messages to control something completely different instead, like wet/dry control.
However, because the MCU protocol is an open standard the idea really is to stick mostly to what the standard says things do. So if you look at a Behringer X-touch and a Mackie Control Universal they look almost exactly the same as far as controls and layout goes. Same with the Icon QCon. Because they all use the same protocol.
Now, the cc121 and the Avid gear aren’t using MCU, they’re hooking into the software differently. With Steinberg/Yamaha controllers there’s proprietary code that hooks straight into Cubase/Nuendo. With Avid’s gear it’s “Eucon”, a protocol that’s available for DAWs, but not for hardware makers. So that’s why you see Avid controllers work tightly integrated with not only Pro Tools but also Cubase/Nuendo, but you don’t see anyone other than avid build hardware with the protocol.
In the end you don’t have to worry so much about whether or not it says “MIDI”, because it’s just a protocol for shuffling data around and you get far more than 128 values sent from the faders.
I will say this though: There’s a big difference in fader quality between the brands and models. You’ll notice it as you move them on the surface, and you’ll notice it by listening to how much noise they make. I personally almost never use the pots for plugin control (I use the trackball) so I end up using almost exclusively faders for volume control. So to me that’s the key feature and they need to feel at least ok. And I hate to say it, but you kind’a get what you pay for here.
What specifically are you looking to do?