Shiryu had a lot of potential on introduction but has been a huge disappointment post skip. The DF alone contributes a lot to that and then add that he hasn't stood out at all(funny given his DF).
People here consider me a huge Zoro fan and I said Shiryu loses to all the YC1 in that vs thread.
I think people just like him though regardless of Zoro. People love swordsman in this manga, Shanks and Zoro are 2 of the most popular characters in the series