But when the Prtestants cannot agree if the free will exists, to pick one example, that is a real doctrinal disagreement.
And yet even Arminians and the Reformed believe that Salvation is by Grace alone thru Faith alone in Christ Alone.
The Orthodox don't believe in the Pope, yet you admit they are Christians.
Faith Alone is false. The scripture teaches the exact opposite. But that is a weak common denominator for Protestantism because, for example, the disagreements of the TULIP are substantial and so the Protestants as a whole cannot be all lead by the Holy Ghost. I don't think any of them are.
The Orthodox and the Protestants are all Christians, but that is where the commonality ends. Apart from the matter of Church governance, the Orthodox hold theological positions that are Catholic. The Protestants, however, teach heresy. Faith Alone is heresy, and it is at the heart of Protestantism.
For the Orthodox to come to the Church all they need is to ask. The Protestants need to recant of Protestantism before they can become Catholic.