Tsunoda scored seventh in last weekend's Miami Grand Prix, cementing RB's sixth position in the constructors' table after team-mate Daniel Ricciardo scored fourth in Saturday's sprint.
While Ricciardo had been struggling to get up to speed this year in the VCARB01, Tsunoda picked up the baton as the team's lead driver over the first five races of the season, grabbing six points in Australia and a hard-fought point on home soil in Japan.
And while the team had been hard at work to make Ricciardo more tuned into the car, team boss Mekies praised Tsunoda for making major progress in his fourth season.
"Yuki has made a huge step this year. In fairness, he made a step between year one and year two, year two and year three. And I think the step he is making now between year three and year four is massive," Mekies told Motorsport.com.
"You see a driver now that is able to not only have the raw speed, which we knew, and he elevated it even more now. But he can execute weekends with absolutely zero mistakes from FP1 to the race.
"It was the case in Australia, it was the case in Japan. And it was not far from that in Miami, to be honest.
"He has made a massive step forward and I think there is more to come, so we are working very hard to make sure we develop an environment where he is able to make these steps. We are very impressed with his work."
Beyond executing error-free weekends, Tsunoda also impressed with his more level-headed demeanour this year, which was a key area to work on after some of the fiery radio messages that punctuated his first years in the series.
"He is getting better [dealing] with the low points," Mekies acknowledged. "China was a good example, he approached it in a rational way and we analysed together and he hit the ground running in Miami.
"So yes, it's a big step forward. It's played a massive role in our current success and we think there is more to come.
"You can also hear it on the radio. He is improving inside and outside the car."
