I honestly do not think Internet Archive even should be archiving such behemoths like Reddit or Twitter. Only thing it should keep would be currently dead sites.
Even worse when people are accessing these posts through Archive even when there is a live copy. A lot of storage and bandwidth wasted.
Archives are ideal for identifying sneaky behavior like that. You never know when an admin might have the ability to delete or edit something without anyone noticing.
But imagine this... an immoral rich human being, who's family got rich by mining blood rubies in south Africa, buys reddit for 50B$. This person fires half the people and refuses to pay the bills for servers and the servers shut down... how will you access your favorite GoneWild posts?
This is all fictional of course.
...but at some point those giant sites may go offline. I see the point of archiving them now for posterity, but you're right. The archive shouldn't be used as a concurrent mirror of those sites for privacy reasons.
I have my browser set up to redirect Reddit links to libreddit instances for that purpose.
True, although I think there usually are either signs or site admins give heads up when site is soon to go under. Doubt Reddit or Twitter will be dead any time soon.