As other people have pointed out, it doesn't seem like the author (or anyone else, perhaps other than you) is suggesting that shared state is a significant reas

As other people have pointed out, it doesn't seem like the author (or anyone else, perhaps other than you) is suggesting that shared state is a significant reason that tsc is slow. But moreover, my takeaway was that the author is making a distinction between a complete rewrite and a port, where the former seems to be any rewrite that just tries to do the same thing (but may be architecturally very different), while the latter seems to be an approach where you attempt to directly adapt the original source code into a new language on a statement-by-statement basis. The latter would likely require the target language to support the programming paradigms which are used heavily in the original source code.