Actually I think "properly tuned" sounds like weasel words, a no true scotsman fallacy. "Oh electron is slow? Well, it is slow, but that's not real electron, see if you were doing things the right way it would be fast"
It just means Electron has bad default settings, it's hard to optimize and you might need to move some parts into C++ if you want good performance. Really the same thing as Unreal Engine, there are absolutely fast games made with it but most are super resource heavy.
It was not "bad default settings", like often with UE5, it was "MS did a superb job making VSCode not dog slow like Atom" and it took really lots of work
It means that you need a trillion-dollar company spending millions of man-hours to optimize the performance, using every trick in the book, and inventing a few new ones to deliver one optimized Electron product