Can someone explain the misuse of cat, which bat solves?
That said, the idea that using cat to show a single file is "misusing" cat is prescriptivist rules-lawyering. There is no technical reason against using cat for non-concatenation purposes. The descriptivist interpretation of cat says using the tool for non-concatenation purposes is fine, since that's how people are actually using it.
However, note that cat is often misused as a substitute for STDIN redirection:
# this creates an extra process that wastes
# time copying STDIN to STDOUT
cat "${inputfile}" | do_stuff
# just connect inputfile directly to STDIN
do_stuff