Spent 2 days at the Orlando Parks in late 2018 doing nearly everything. USH looks mostly like a mix of the 2 parks w/ a few unique things like the Studio Tour. Is this accurate or am I missing something?
Pretty much accurate, but I will add that the park is in a really cool location and that the Studio Tour truly is something special that simply doesn't exist anywhere else (though you can experience components of it in Orlando and the other Universal parks).
It's fun if you go, but I wouldn't necessarily say most of it is essential if you've done Orlando.
I agree with the PP. If you've done Universal in Orlando and are visiting CA with only so much time, I'd highly consider allocating that possible Universal day to something else. Southern California has so many unique things to try.