Capito officially confirmed in Austin on Saturday that the Williams Academy driver will replace Nicholas Latifi next season, assuming that he secures his FIA super licence after the Abu Dhabi F2 finale.
Sargeant will become the first American F1 driver since Alexander Rossi raced for Manor in 2015.
His graduation comes after the controversy over Red Bull’s unsuccessful efforts to land a super licence for IndyCar star Colton Herta.
A US driver on the grid is seen a coup for the sport by F1 bosses Stefano Domenicali and Ross Brawn, especially heading into a season that will see three American races.
Sargeant will also clearly help Williams owners Dorilton find partners in the USA.
However Capito insists that the 21-year-old has been fast-tracked through the ranks on talent alone.
"It is a good for F1 to have an American driver,” said Capito. “But we didn't pick Logan in the Academy because he's American, we picked him because of his success and his past in racing.
“And if we take the kids or we put into the Academy, it's the objective to get them in the F1 car. If you have a young driver who is ready for F1, and you have the seat, then you have to put these young drivers into the seat, otherwise, you've done something wrong.
“And that's why we came to that conclusion that is the right thing. And that Logan is American, I think it's nice to have, but it's not the initiation of the decision.”
Asked about the obvious marketing benefits and the timing of the announcement he said: “Yeah, we're not stupid, are we? We had to put this out at the right time."
Capito said that Sargeant became a serious candidate for a race seat after he scored his first F2 feature race win at Silverstone.
“I think from Silverstone onwards, we said ‘Okay, Logan is ready to get in F1.’ Of course, that was so early in the season that you can't commit, because there's so many things to come, and it went up and down.
“So we had to talk to other drivers as well and sort out the options. And that helped us also then in taking the final decision, and also cover the risk if Logan for whatever reason would not get the superlicence points. We believe he will get the points.”
Asked if Sargeant had progressed faster than expected Capito said: "Oh, not really. But you never know how the development is.
"And from my history, I'm known to get young drivers in quickly. Because that's the best way to find out what the potential really is, and not parking.
“If you see that somebody is ready, like Logan this season, then we can take that decision. He wouldn't have been lost if we had decided he needs another year in F2. Then we would have done that as well.
"But we see that coming in as a rookie, winning races and showing that performance in qualifying, it's the right thing to step up."
