Well... I'm going to guess that the largest kernel written in PL/I was at least one order of magnitude smaller than Linux, and probably two orders of magnitude smaller. I'm also going to guess that it was never subject to a 2020 state-of-the-art fuzzer. (I'm even going to guess that it never had USB support.) So, while you may have a point, your comparison is hardly apples-to-apples.
