I’m not the biggest fan of electron generally speaking but I don’t agree with your argument that Electron is too slow to work as a terminal emulator. Yes speed matters, but not nearly as much as you claim. Commands are run as separate processes so as long as the terminal reads from its PTY fast enough not to block those processes, which in all bar a very few edge cases it will be, you’re not going to experience any difference in performance.
Besides, if you’re concerned about millisecond latency, then the issue you actually have is with multimedia content being rendered in the terminal rather than Electon itself. So no terminal emulator of this generation is going to meet your needs irrespective of what technologies it’s built from.
Edit: downvoted for stating a fact. Maybe I should have also stated that I’ve also been working on this exact problem. In fact I’ve already got a shell that provides the CLI parts and been playing around with different technologies to handle the multimedia parts of the terminal emulation. It’s a harder problem to solve than people hand wave away when they complain about electron (hence why I only have a shell available for public use at this stage).