Yes, the RC system is designed to alleviate the issues, or at least make it a better experience. Low SP accounts will of course run out of RC. There's never going to be billions of accounts on a freemium blockchain. Freemium means - you have to power up a certain amount to use it. Steemit Inc can cover you temporarily with delegations, but that's not the intended long term design of the platform; hence why they call it freemium.

Facebook has a massive network effect, and there are no bandwidth concerns to think of as they can easily ban spammers and generate revenue from advertising.