The Aprilia rider struggled to ninth at Phillip Island on Sunday due to an apparent electronics issue, which has left him trailing 27 points in the championship to new leader Francesco Bagnaia with just two races to go.
Espargaro has been in the title fight all season since he took his maiden MotoGP victory in Argentina but says "it's never been" the case that the vastly improved RS-GP was anywhere near the level of the Ducati.
With six of the eight Ducatis finishing inside the top 10 at Phillip Island, Espargaro admits this is "frustrating" as the bike is good enough to allow "everyone who rides it" to be strong.
"It's funny because not too long ago, three, four months ago, everyone was saying the Aprilia was the 'new Ferrari'," Espargaro said.
"I knew the bike that I had, I know it's a good bike, I know we improved the bike a lot. But it's not at the level of the best bike of the grid at all.
"It's never been like this, but they made many mistakes in the beginning of the year and they paid it now. But today the results of the Ducati, it's ridiculous. It doesn't matter who rides the bike, they are in the top six. It's very frustrating."
While Espargaro still has a mathematical chance at winning the championship, he admits during the flyaway run of races that Aprilia "proved we are not together as a team" and "not at the level to fight for the title".
"More difficult," Espargaro responded when asked what he thought of his championship hopes now.
"I think that in the last three races we proved we are not together as a team.
"We are not at the level to fight for this title. We've conceded many, many points, because at the end in the last three races we scored eight or 10 points (12 points).
"This is ridiculous if you want to fight for the title. This is the problem. It's still possible, I'm really proud about my championship.
"There's two races to go and Aleix and Aprilia are still in the game for the title.
"So, I'm proud. But with Pecco and Ducati's form, with one race of advantage [in terms of points] on me it's going to be very tricky."
