He's always been using literally the least amount of power required after the timeskip vs antagonists. It's evident and closely linked with Mihawk's philosophy and teachings.
He never tries to be flashy unless required after postimeskip and has always held back.
Dismissed Hozukyu as fodder and told him to stay away.
1 sword vs Hordy.
1 sword vs Monet.
Santoryu and toying with Pica until required to do so or when his friends were in danger, in which case he pulled out 2 high level/ secret techniques.
Only took Wano seriously since the stakes in place were kind of insane.
What Zoro says to Luffy isn't to do with power usage, if it was he would have insisted luffy to use gear 4th and end everyone that came before Doflamingo.
It's the fact the Luffy is goofing around and making jokes, while Zoro himself got caught off guard by the Whisky brothers in the new world.
He's yelling at Luffy not to drop his guard or be taken by surprise.
In Egghead, he trusts Luffy and Sanjino to take care of things. He knows Luffy is where Saturn is via haki, but I guess he shouldn't have trusted Sanjino to take care of Vegapunk.