and many ksh scripts outside of Linux uses that syntax
What does Korn Shell offer over Bash shell, again? I've never used it, other than encountering a few legacy scripts on customer systems written in ksh that stopped working when they migrated over to RHEL/Centos7 and ksh was no longer installed by default.
Discipline functions, floating point arithmetic, compound data types etc. Original KornShell is still more powerful programming langauge than bash.