The Grove squad has been unable to compete with any other team during the opening five races of the season, as it searches to fix the problems that have seen it decline in recent years.
Russell pointed out that the gap to the nearest car in Barcelona was reduced, which left him encouraged that the team can extract more from the year.
"It's definitely not a write-off," he said. "The fact is, we've got a huge amount of issues at the moment which we think we can resolve.
"Barcelona was the first real race of the season, in my opinion. Australia was a street circuit, Bahrain is a very specific circuit at night.
"China was freezing cold and Baku was Baku, we knew it wouldn't suit our car as we are slow on the straights. But Barcelona was probably the first true test, and we were four-tenths away from the next car."
Russell crashed at the end of the final practice session before qualifying but still managed to emerge for qualifying and set a respectable time.
"With all the issues that we've got, considering in FP3 when the guys got the car ready in an hour and a half, we didn' bring as many upgrades as the other teams, it's far from a write-off.
"If we do the job properly, we've got potential to not only close the gap but to fight with some people."
Russell added that it was difficult to predict if Williams can score points in 2019.
Last season, when it also ran for most of the year as the grid's backmarkers, it managed to score 7 points between Lance Stroll and Sergey Sirotkin.
"On merit, who knows," Russell commented. "Like I said, it's definitely not a write-off and I think we can salvage something from this.
"We've definitely got a lot of performance in pocket but is a lot a second, 1.5 seconds? We don't know yet."