Paddy Lowe has claimed that Williams must endure more "pain" before solving its problems.
The once-great team now has the slowest car in Formula 1, with technical boss and shareholder Lowe declaring to Auto Motor und Sport that a new front wing has helped slightly.
"But as you start digging, you find more and more problems. We have to make up a lot of ground," he said.
Lowe acknowledged Williams's problem of trying to fix the 2018 car while simultaneously preparing for the considerable rule changes for next year.
"In the meantime, we have to endure the pain until there is a solution," he said.
"It's mainly aerodynamics but also more than that. The car lacks stability. We've fallen behind compared to last year.
"We hope to make some more changes after the break but it won't be half of what we need. Still, we're hoping for a better second half before we concentrate fully on the 2019 car."
Lowe, who later worked for Mercedes, compared the situation to McLaren in 2009, when he led the efforts to fix a badly-born car.
"It's not directly comparable, but it shows that if everyone works purposefully, with discipline and while staying calm and united, you can pull out of it. In the end it's a technical problem, and all technical problems are solvable," he said.
"It's better for any team to have two multiple world champions," Lowe said. "But our problems have nothing to do with the inexperience of our drivers.
"They're doing a good job in a difficult situation. The car would not be better if we had other drivers."
Williams remains bottom of the 2018 constructors' championship with four points.