[error54]

That's pretty close. For our use case (and many others), the biggest culprit for increased TTI is the sheer size of the JavaScript payload and the time the browser takes to parse the whole bundle[1]. We still use React and other libraries on the server to generate the HTML but rather than sending all that JS down, Tony worked out exactly which client interactions still needed JS and wrote those in plain JS which resulted in a big TTI win as the browser simply had less data to parse.

1- https://www.youtube.com/watch?time_continue=1297&v=M1qm-AWWu...