Simply using cat to dump a single file to STDOUT is technically a misuse because cat is theoretically intended to concatenate files. This 'misuse' is 'solved' by bat because bat seems to be primarily intended for its syntax highlighting and git-related features; according to bat's docs, cat-style concatenation of files is intended for drop-in compatibility with traditional cat.
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 "${inputfile}" | do_stuff
# just connect inputfile directly to STDIN
do_stuff <"${inputfile}"
# or if you want to keep the input
# at the start of the pipeline
<"${inputfile}" do_stuff
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: