A common story with JIT languages is to go back and forth between having a bytecode interpreter and not.

The paradox is that when the interpreter is fast enough then you delay JIT because it takes longer for the amortized cost to be justified. But that also means the reasons for that high amortization cost don’t get prioritized because they don’t really show up as a priority.

Eventually the evidence piles so high nobody can ignore it and the code gets rearranged to create a clearer task list. And when that list runs out they rearrange again because now that other part is 2x too slow.

Personally I’d love to see a JIT that was less just in time. Queuing functions for optimization that only get worked on when there are idle processors. So there’s a threshold where the JIT pre-empts, and one where it only offers best effort.