Compilation / type checking depends on a lot of trees of typed data, and operating on those tree nodes. That's something where a statically typed language with custom data structures that allows for optimised representations makes a big difference, and where a lot of the fancy optimisations in v8 don't work so well.
There is a reason Typescript moved to a typed language.
Let's hope you're right and that translates to even higher performance for Ty compared to Pyright. There are of course many variables and gotchas with these sorts of things.
There is a reason Typescript moved to a typed language.