He also pretty much beat Hawkins.
Who, Zoro? No he didn't beat Hawkins! Hawkins was merely using his DF ability and that was just enough to keep Zoro busy, Hawkins wasn't even using the full capacity of his DF abilities needless to say Haki. Also, the fight ended with Hawkins leting them escape, he didn't want to pursue them since in that case he would need to fight against both Luffy and Zoro, and Hawkins is smart boy so he knows that he has Zero chance against both Luffy and Zoro, actually if read the newspaper then he knows that only Luffy by himself can mid/low diff him.
Why did it diminish with Killers defeat
Because it shouldn't have happened if Kidd is truly Luffy's rival, if they are truly rivals then the fight should have ended in draw (like Roger vs Whitbeard) and Luffy vs Kidd should be draw too. Whitbeard wasn't Roger's rival because he was inferior to Roger but actually the opposite. Whitbeard was Roger's rival because he was equal to Roger, most of his fame comes from the fact that he was the only one who could go toe-to-toe with Roger.
Now the reason why it demolished my hopes is that first, the supernovas weren't impressive so far and second, Oda himself admitted in an interview that supernovas aren't that much important and that he's surprised that all of them are still alive. But in the same interview he said that kidd is the only one on whom he has plans in the future which sparked hope in me for kidd and his crew since Oda has been very clear that Law is inferior to Luffy, and his crew is inferior too. With Killer being defeated by Zoro means that Oda wants to go with chosen one plot and even though I don't like it but I can accept it in case of Luffy (cuz he's the main character) but I can't accept it in case of whole crew, which is where Oda is going with this. The same thing happened in Naruto when at the beginning there were a lot of rivals for the main characters and it was so interesting to watch them all, but later on, all those characters became a side characters with only purpose to make Naruto and Sasuke look good while the story concentrated around Naruto and Sasouke secret gay love.