Well, they think that it's a case of Shanks being Luffy and Zoro being Mihawk, which isn't really right because Shanks is just one of four pirates that Luffy needs to overcome, and he's not the strongest one either.
Plus they make the mistake of thinking relevance = strength- again, not true. Shanks is by far the more important character, I'll never argue against that. But that doesn't mean that Shanks is stronger than him, anymore than it makes Shanks stronger than Whitebeard or Kaido.
And the major one of the idea of Zoro being one of the strongest characters in the series causing people to break out in hives and start foaming at the mouth.
Ultimately I just come down on Mihawk and Shanks being dead equals like Roger and Whitebeard until Shanks lost his arm and got a bit weaker. Mihawk is raging because he never really got his title the proper way and that's why he was the way he was at the start of the series, Shanks is still one of the strongest people in the world but knows he's not who Roger was waiting for, so was happy to sacrifice his arm and pave the way for Luffy to come along.