Max Verstappen has been the only "flawless" driver on the 2019 grid so far.
"Hamilton, Bottas, Vettel and Leclerc have had ups and downs," he told Auto Bild. "Only Max was flawless and always got the maximum out of the car -- sometimes even more," he added.
"He is absolutely ready for the title. In Barcelona, we now have to prove that we are too."
Marko said Red Bull has prepared upgrades for Barcelona that should solve what he earlier described as the car's "aerodynamic problem".
"So far, missing downforce was our problem," he said before the Spanish GP.
"The design of the car was due to the lack of engine performance of our former engine partner, so that we had to design for efficiency," Marko explained.
"So we have been losing time in the corners. But Honda has significantly increased its performance and we can now respond."