Why is #!/usr/bin/env bash not working on my system?

ls -lL /usr/bin/env shows that the symbolic link is broken. That explains why the shebang line isn't working: the kernel is trying, and obviously failing, to execute a dangling symbolic link.

/usr/bin/env -> ../../bin/env is correct if /usr and /usr/bin are both actual directories (not symlinks). Evidently this isn't the case on your machine. Maybe /usr is a symbolic link? (Evidently it isn't a symbolic link to /, otherwise /usr/bin/env would be the same file as /bin/env, not a symbolic link).

You need to fix that symbolic link. You can make it an absolute link:

sudo ln -snf /bin/env /usr/bin/env

You can make it a relative link, but if you do, make sure it's correct. Switch to /usr/bin and run ls -l relative/path/to/bin/env to confirm that you've got it right before creating the symlink.

This isn't a default RHEL setup, so you must have modified something locally. Try to find out what you did and whether that could have caused other similar problems.