[freebs]

I agree with you that this definitely a rendering content in JS problem.

Most of the SEO experiments with increasing page speed from bad to average or great have shown a very small increase in rankings. We're talking one small signal in the whole algorithm. In this case, trying to go from average or good page speed to great page speed just for rankings is quite foolish.

If they want page speed to be the best it can be, and they absolutely must render the whole page in JS, they should have at least tried to use PhantomJS or something else to render the page properly for googlebot.

There's always the traditional options that can increase speed: minimize the amount of JS, increase the quality of JS written, less HTTP requests, proper DB calls, image sizing, proper caching, etc.