Linking MIDI knobs with their VST targets via the Focus interface is unnecessarily obtuse - there is a lot of clicking back and forth. Re-assigning a knob is also problematic - you must first turn the hardware knob that is already assigned (unintentionally changing its current VST target's value), click the new desired VST target and then click the "link" button.
It would be more efficient and intuitive if clicking and holding the mouse on your VST knob / slider / etc entered a "Quick Assignment Mode", in which case it would listen for incoming MIDI CCs and immediately link.
This mode should be optional, as the majority of time you are clicking a VST's controls you are not attempting to assign hardware controllers. The option to momentarily engage "Quick Assignment Mode" should be assignable to key commands and/or always function on Mouse 3 (middle click).