during Western Schism (3 claimants to Papacy, Avignon etc…) there was One True Church with True Pope leading it and others were pretenders.
How did they determine who was the True Pope and True Church? When all three Popes looked the same and their followers were all Catholics?

(Hint: the answer is the Council of Basle, which brought conciliarism to the fore, which would look like a point for the Eastern polity, except the Pope could never accept that, so he conveniently nullified the canons that pertained to a Council having authority over the Pope, and declared conciliarism a heresy, causing quite a mental dissonance, for it was a Council’s authority that ended the Schism and confirmed the true papacy in the first place).
Jus’ sayin’
Problem is that dogma of both Churches actually contradicts this view.
But did not the dogma develop after the Schism as a justification for our quarrel? Even the Council of Lyon which was the first Council to attempt reunion and the Council which was notable for declaring that every creature must be subject to the Roman Pontiff, was held after the Schism, while the Constantinople Council held in response was to declare that Roman Catholics had to be rebaptised to be admitted to Communion with the Eastern Churches.
Catholicism has Holy Tradition full of devotional, ascetical, mystical understanding of the Church and sense of otherworldliness. Whether people follow that or not doesn’t exactly depend upon Eastern Orthodoxy
Agreed insofar as the West’s own spirituality doesn’t depend on Eastern Orthodoxy.
Disagreed in the sense that for the most part, the Orthodox have preserved Holy Tradition, while since the New Theological Movement and Vatican II, the Catholic Church has discarded or shall I say, inconveniently ignored, her Sacred Tradition, persecuted those who hold fast to her Traditions (thinking SSPX, FSSP, ICKSP, and the traditionalist movement) as handed down to them, and become permeated with worldliness, corruption and a phronema (mind) that is puzzling to say the least to the Orthodox.
I am certainly not discounting the many pious Catholics that I have encountered, but the level of catechesis, the sense of piety, that the Orthodox have maintained even among the laity is certainly astonishing by comparison.
I say this with heaviness of heart, wishing that it were not so, and praying for the restoration of Catholicism to a resurrected, transfigured state. That is Catholic Church, I hope and pray, once cleansed of modernism, that will be the Church to reconcile with the Orthodox. That is the Catholic Church I would consider entering communion with.