Sorry but it seems that you have no idea how netflix really works.
The frontend is anything but java (the website uses javascript, they have mobile apps, not sure what they are written in, but besides android having a few necessary wrappers, these are also not java applications).
You don’t see the backend and they do different things between different services so not much point in comparing them - that’s a huge, complex, partially cached-at-your-ISP even network infrastructure.
Besides, Java itself is very fast and is itself no reason for an applications’ (especially network-related) bad performance. It literally runs like half of the internet, with basically every other top 100 IT companies having business-critical infrastructure dependent on it.
I never saw BE which sends so much requests to FE for user info. Someone just has no idea how to use Java without making CPU wild.