I think Bun helps with the memory pressure, granted this is relative to V8. I'd pushback on the certainty with the reality that TS provides a significant drop in entropy while benefiting from what is a sweet spot between massive corpus size and low barrier for typical problem/use-case complexity. You'll never have the fastest product with JS, but you will always have good speed to market and be able to move quickly.
It's plenty usable. Most of the problems with the claude TUI stem from it being a TUI (no way to query the terminal emulator's displayed character grid), so you have to maintain your own state and try to keep them in sync, which more than a few TUIs will fail at at least sometimes, hence the popularity of conventions like Ctrl+L to redraw.