The bin/doctrine-dbal.php file is not an executable file. Adding them as a bin in composer.json means that any composer install will trigger changes in the source when using symlinks because of the chmod. This makes things a pain when installing from source.
Thus, there is no valid reason to add it. It is absolutely not necessary when using a composer install. The issue requesting it previously is actually an issue in Laravel which replaces the proxy file/symlink generated by Composer with a copy of the original file, which of course cannot work because of paths used in require. But copying a second file does not help for that (unless in very specific cases). It only moves the issue until the next require call.