Nope. I don’t believe it.
I don’t think a few weeks of “brainwashing” would lead Oliver to try to kill Diggle or Nyssa. Or capture and hurt Lyla. Or release the Alpha/Omega weapon.
It doesn’t make sense.
Oliver has been imprisoned before. Tortured before. He spent five awful years in captivity, or on the run, or in solitude, while everyone else thought he was dead. Suffered years and years of pain and danger and horrific circumstances. He’s survived arrows, gunshots, and the blade of Ra’s al Ghul through his chest.
He’s gone up against all kinds of villains and evil and prevailed through it all to protect those he loves, right the wrongs in Starling City, and protect innocent people.
You can’t just turn all that off like a switch.
Oliver is SO much stronger than any League voo-doo.
He’s gotta be playing the League. Pretending and going along with everything to take over for Ra’s and earn Ra’s’ trust. And then the minute Ra’s has his back turned…BAM! OLIVER DESTROYS THE LEAGUE FROM THE INSIDE OUT!
Plus, the show is called Arrow. Not Ra’s al Ghul.