Uh, what have notifications anything to do with RSS? Practically all all web services and mobile apps for it offer them.
Social media, on the other hand, is an alternative solution to the consumption of information, not inherently a better form of aggregation.
It is mainly the addiction to social feedback that attracts people to social media, while RSS is a boring stream of data you've specifically decided to process.
RSS was created in 1999, when short of visiting a website it was the only way to get updates about new content. Now, there are other ways which people already use and like, addiction or not.
When RSS was created is irrelevant, when its age does not hinder innovation in its implementations. It's like saying email or phone calls are obsolete because social media has taken over.
Social media, on the other hand, is an alternative solution to the consumption of information, not inherently a better form of aggregation.
It is mainly the addiction to social feedback that attracts people to social media, while RSS is a boring stream of data you've specifically decided to process.