The phrase 'without overstatement' is correct and usable in written English.
You can use it to draw attention to a fact or idea that might otherwise sound exaggerated. For example, "It was undoubtedly a difficult challenge to complete this project, without overstatement."
One can say that without overstatement.
He speaks, without overstatement, of a potential 100m customers.
Oh Rhyne's Polonius had a wry jocularity; Bruce Barton, as Guildenstern, suggested vaudevillian dimensions without overstatement.
It is, in effect, an acting job, and Mr. Kuerti undertook it gracefully and without overstatement.
"They'd like to name the movie 'Julia and Tom Are in This Movie,'" Mr. Hanks said of the studio's marketing executives, not without overstatement.
It can't be easy these days to be a 30-ish female American cellist not named Alisa Weilerstein, but Julie Albers is a fantastically eloquent player, with an elegant sound that is full of emotion but without exaggeration or overstatement.
Without hysteria or overstatement, she reminds us that folksong taps a collective history that we ignore at our peril.
"Soft Fruit" belongs, however, to the divine Ms. Drynan, who plays a dying, unfulfilled, ordinary woman without embellishment or overstatement but with mischievous reserve and surprising sensuality.
They became witnesses to the day when the cascading accusations about wrongdoing by newspapers in Mr. Murdoch's British stable brought not only the withdrawal of his $12 billion bid for British Sky Broadcasting, but also what many politicians hailed, perhaps without too much overstatement, as the day when the country's long-skewed democratic balance began to be restored.
The Emerson took full advantage of that, couching all three works in a warm, finely polished sound and mining them for drama and intensity without ever lapsing into overstatement.
It would be an overstatement to suggest that without KILLER FILMS, the New York-based production company founded by Christine Vachon and Pamela Koffler, there would be no American independent film movement.
