Live reload gets you most of the way for UI programming, yes.

REPL is the secret sauce for writing any time of program, not only UI. It lets you explore, play, test, inspect and break things very quickly and without losing context before you find the final shape of your code.

I can’t live without it, but it’s hard to explain the benefits to the people who have never experienced it. You have to try it to really be convinced

Here is a tiny demo of how I usually use it to build a program https://tonsky.me/blog/interactive-development/