I can talk about the second question, the first one is better address by the article I linked to above but in short, it's not a problem. It's not about the number of follows, it's about the matrix of follow (being followed by someone with high UA). For example, I have 17000 follows but I only follow about 100 people. That signals that my content is appreciated by lots of people. My follow has much more weight than Joe Blo who just started. But if Joe Blo writes awesome content, he's start ranking when people like me start to follow him.

IF someone who has a high UA start writing crappy content, then people will stop wasting their follow on them and follow someone else with better content. UA is dynamic and constantly changing since the sum total of all UA is 1. Someone whos' a top dog today could be at the bottom of the barrel when they start writing crappy stuff.

Did other platforms used that technique? Google!