Mercedes has been left with choice but to use the development of the W14 like "plasters" to combat the "nasty" car, according to Toto Wolff.
The eight-time champions were comprehensively beaten in the Sao Paulo Grand Prix weekend with a combination of high tyre wear being mixed with slow straight-line speed to make for a miserable event.
Lewis Hamilton was only eighth in the race with George Russell retiring, with Wolff describing the weekend as the worst of his 13 years in F1.
The Brackley squad has been hamstrung by at first doubling-down on its flawed zero sidepods concept with the W14, with resulting upgrades changing the architecture of the car, but not the on-track performance.
Worryingly for Mercedes, the likes of Aston Martin and McLaren have been able to turn their fortunes around while the team cannot, with Wolff firm that its performance was "not on."
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Wolff baffled by Mercedes lack of pace
"It is totally baffling and at the same time, unacceptable for all of us," Wolff told media including RacingNews365.
"We have a proper structure, solid team and we didn't look like a solid team.
"Within three consecutive races, you're finishing a strong second in both of them [on the road] challenging Max, and then a week later, you end up nowhere. I believe it is just not on.
"When I look at our competitors, even between the cars, Red Bull doesn't get things wrong very often. Aston Martin, within one week of being outside of the points to having a solid podium.
"McLaren, in the first part of the season, it was not making it out of Q1 at times, and [in the race], it was hunting Max.
"[The car] is sometimes a nasty surprise box for all of us - and we got it probably as bad as some other teams got it.
"The development on this car is more plasters that we have put on, and that is not right.
"It shows that it is so unpredictable and can swing either way, and you can be six, seven or eight-tenths off when you just tip over the edge."