What do you mean?
Zoro has retained the same personality as always. I see no change, besides the fact he is now powerful as hell.
Competing to see who could kill more fishes. He did it before on the Giant island aganist Sanji seeing who would kill the biggest animal.
Ranking them on order of how the arrived, he has been doing that with Sanji for a long time on who was stronger between the two, by saying who took out who.
He has always been lazy, the only difference with him is that he doesn't get pissed at Luffy stupidity like before. Hell in the end everyone has the same personality. Even Ussop after becoming so strong, he still acts like a fool.
Plus, I wouldn't say he is over confident, if anything he has less confidence now. He trained under Mihawk, which is why he is so strong now, but this means he saw the HUGE gap between him and Mihawk. Remember even though he is with Luffy, he is really the only one with a true goal on the crew to become the strongest swordman, and for that he needs to defeat Mihawk.
And again, besides Luffy, he has shown the most grown in terms of strengt than anyone else. Remember how when Don Krieg appear, Mihawk showed up for the first time. He cuts a galleon in half and everyone is impressed, and Zoro even calls cutting the Galeon in half "The ultimate power". When Zoro reappears, he cuts a galleon in half. Pretty much stating that he has become one of the strongest Swordsman in the OP Universe. I mean they have only used the word Galleon on the series 3 times. Skypedia arc, Don Krieg arc and the current one. Which makes it obvious Oda wanted to point out the huge growth he went through.