If you need to memorize and intuitively and instinctively understand the whole language (including all possible external libraries) to use it at a given organization, then that organization has serious problems.

I have personally mentored competent programmers with no Perl background, and it takes a lot less than 5 years for them to become productive. It only takes a couple of weeks, max. Over time they will become more productive, but it doesn't take long.

In fact I'd wager that a good programmer with no Perl will become productive working in a good codebase far faster than an OK Perl programmer will. (In a bad codebase, of course, nobody is productive.)