Yes, as a former Convert to Orthodoxy and revert to Catholicism, I can disprove the claims of the Orthodox Church on-
- Its possession of the marks of the true Church.
- Its objection to the filioque clause.
- Its objection to the Latin notion of Sanctifing grace.
Let’s just start with these three and you can pick which one you find most threatening to address.
- The true Church founded by Christ is One, Holy Catholic and Apostolic. It possesses unity in faith, sacraments, teaching and discipline. It is Holy because its founder is Holy and its members are called to be Holy and it possesses the means of holiness for others. It is Catholic because it is found all over the world, which is a necessary condition of the true Church of Christ, and its teaching is that which has been held every, always and by all, and it is apostolic because it possesses apostolic succession and holds to the apostolic teaching.
Orthodoxy, while having a semblance of unity, and while we all have our dissenters, certainly is at least wounded in its unity, by not having that which its own saints would admit is useful for it- namely, communion with Rome-
“We should not contradict the Latins when they say that the Bishop of Rome is the first. This primacy is not harmful to the Church. But only let them show that he is true to the faith of Peter and his successors; then let him have all the privileges of Peter, let him be first, the head of all and the supreme hierarch. Only let him be faithful to the Orthodoxy of Sylvester and Agathon, Leo, Liberius, Martin and Gregory, then we too shall call him apostolic father and the first among hierarchs; then
we will be under his authority not only as under Peter, but the very Saviour Himself.”
(PG 145, 120 AC) St. Symeon of Thessaloniki
Regarding the mark of Holiness, they certainly possess true sacraments that can convey grace, but they are objectively offensive to God by being administered in a state of schism. They certainly number many holy men in their ranks, but their fall from unity condemns them.