How performant are the arduinos as keyboard controllers? E.g. for a gaming application
Which Arduino? The low-end ones don't have USB interfaces.
Latency will mostly be determined by the host's USB polling speed and the keyboard firmware's scan rate across the keyboard. Pretty much any controller will do an equally good job; it's often done by low performance 8051 chips.
Similarly, &quot;ghosting&quot; is an inherent problem with keyboard matrixes that must be solved by adding diodes to the scan matrix and is independent of what controller is used.