The phrase "although he was mostly" is correct and usable in written English.
It can be used to introduce a contrast or exception regarding someone's state or behavior, typically followed by additional information.
Example: "Although he was mostly quiet during the meeting, he had some valuable insights to share."
Alternatives: "even though he was primarily" or "despite being mostly".
He began to define himself as "omnisexual," although he was mostly attracted to women.
Although he was mostly treated politely Thursday, his early struggles and recent comments did not endear him to some fans.
In Pineda's last start during extended spring training, he threw as hard as 95 miles an hour, although he was mostly at 93 or 94 m.p.h., Cashman said.
Although he was mostly self-taught, his first audition in 1988 resulted in the tenor lead as Alfredo in Glyndebourne's touring production of La traviata.
He later studied conducting with Franz von Hoesslin at the Munich Academy of Music, although he was mostly self-taught as a conductor.
And although he was mostly bowling spares at first -- not winner material -- he never cursed or scowled or stomped his foot.
James Gregory, also spelled James Gregorie (born November 1638, Drumoak [near Aberdeen], Scot. died October 1675, Edinburgh) Scottish mathematician and astronomer who discovered infinite series representations for a number of trigonometry functions, although he is mostly remembered for his description of the first practical reflecting telescope, now known as the Gregorian telescope.
He was mostly peripheral, although he was still able to conjure an impudent moment when he flicked the ball with his heel and it bounced off the top of the crossbar.
The ship spent most of 1943 in the northern Norway although she was mostly inactive because of fuel shortages.
Since the terrorist attacks in Paris last month, Trump's campaign has focused largely on concerns about national security although he's offered mostly vague details as to how to combat Islamic State.
Shea: I think Fran Vazquez may make the move to Orlando and provide something they need -- and although he was required to play mostly in the paint in the ACB and Euro league, he is a true power forward with a decent shot.
