Personally, I think the retweet model is slightly more problematic than the upvote model. For one, upvotes have an equivalent downvote (usually), which a retweet doesn't. If a famous account upvotes a post, and a I downvote a post, they basically cancel each other. If a famous account on retweets a post, then millions more will see it thanks to that one button click, and nothing I can do balanced that.

Facebook also thrives on a similar "re-share" model, which leads to the most toxic content spreading extremely quickly and bouncing to new audiences, whereas no matter how many times I upvote this thread, only a few % of the world browses HN.