Are you sure that Netlify homepage uses react? I have react developer tools installed and it indicates no react presence on netlify's (very plain and simple - I mentioned complex apps in my initial message, but that is another thing) homepage.

Another example could be Facebook which qualifies into "complex apps" category and at the same time is very well known for sluggish performance.

Not sure if that's a typo and you meant Netflix or not, but did you know that Netflix actually gave a presentation about removing React from their homepage, and got an incredible performance boost from it? I suspect something similar in the case of Netlify, if you're referring to them.