The Ferrari driver finished third on the podium behind Lewis Hamilton in second and race winner Valtteri Bottas.
"Boring, isn't it?" Vettel said (quoted by BBC).
"So boring. It's not just four races. It has been four years, more or less.
"[We have to] work harder, work better. We are pushing as hard as we can.
"But you need to respect that they are doing phenomenally well and getting their cars most of the time in the right place.”
Mercedes have won the past five constructors and driver titles, but Ferrari looked to be the team to beat and dominate after an impressive winter testing.
A few problems and errors over the first races have left them behind the silver arrows looking for a solution.
Vettel is confident in his team and believes they will solve the problem to compete for the title.
"But I'm confident. I believe in this team and I know we can improve,” Vettel said.
“I think we have a good car. We just haven't managed yet to put it always where it belongs, so it is difficult to have the trust and the feel, but I am sure it is going to turn around.
"It's like a Rubik's Cube. We just need to solve it.
"We have a lot of people who can do the Rubik's Cube in a couple of minutes. We have really clever people but we are working on a large-size Rubik's Cube."