The Mercedes-powered team are seventh in the constructors' standings, but level on points with eighth-placed Haas and only two clear of Alfa Romeo.
"The car we have, that’s it," Vowles told reporters at the Dutch Grand Prix.
"Unlike Haas, who I think are a fierce adversary, we don’t have anything more coming for the remainder of the year. So we have to try and pick up the points that are going to be available to us when they're going to be available to us."
Vowles accepted that Williams might lose out to their rivals in the short term but said the team were looking to be more competitive in the longer term.
"At the moment, we're in a fierce battle for this 10th, ninth, eighth, seventh. I want the team, for them, and for me as well to be in a fierce battle for positions above there," he said.
"You can't do that by continuously developing what you have at the moment. You do that by thinking forward into the future, and that will have a cost associated with it, potentially even going backwards for a year, but to go forwards again in the future."
Although the rules are stable between this year and next, Vowles said there was too much the team needed to change for 2024.
"I’d much rather focus on breaking systems and rebuilding them rather than trying to make do," he added.
Vowles said highly rated British-born Thai Alex Albon (27) had the potential to win races while American rookie Logan Sargeant (22), whose F1 future remains uncertain, had to keep developing and narrowing the gap to his teammate.
"The rate of learning has to increase now," he added. "He’s aware of all of that, and I think he has a huge maturity beyond his years."
