"has been foremost" is correct and usable in written English.
You can use it to describe a person or thing that has been in a position of primary importance or significance. For example, "John has been foremost in advancing technology in this field over the past 10 years."
The caliber of his dancers has been foremost among his concerns.
China is clearly worried that the Japanese and Korean positions on financial issues are taking away the initiative in regional cooperation from China, which has been foremost in pressing trade pacts.
Countering this, A.D. Redmond of the Overseas Development Administration (the predecessor to the Department for International Development) wrote in November 1993 to the British Medical Journal: The Overseas Development Administration has been foremost in supplying medical and humanitarian aid to the people of Bosnia throughout the conflict .
However, altered in blood flow has been foremost observed during exercise or mental tasks.
"This seems to have been foremost in the mind of the designers, while the collection came second," Mr. Beschaouch said.
An England player who had been foremost in the taunting challenged Cullis to ask a Frenchman for directions.
It is not known which cities were important centres of production; but the Eastern capital, Constantinople, must have been foremost among them.
The question that had been foremost on the minds of fans — whether this would be the week Mickelson supplanted Tiger Woods atop the rankings where he has spent the past 501 weeks — had given way to another, admittedly hypothetical, question.
Prominent among them was Boris Johnson, the popular if sometimes buffoonish Conservative mayor of London, who had been foremost among those protesting at the five days of mayhem that followed the May 6 general election.
Those who have been foremost in the fight against Ebola in west Africa, especially Médecins Sans Frontières, have been calling for such a commitment by developed nations for weeks now.
It should have been foremost, especially on that in-like-a-lamb evening in March, a month or so after his stroll with Sarah, when Kromer improbably pried Renee and Luna loose from a dull celebration, held at a pub just a few blocks from his building (some underdog had passed his orals, on second attempt).
