They dispensed with Roman claims in order to return to practices taught them by the missionaries from the East who proselytised them. These missionaries from the East were Cyril and Methodius. This they claim themselves, corroborated by the post-Soviet Bloc Czech church, which survived underground for the duration of the Soviet Bloc era, much as the Unitas Fratrum did for a century during Roman persecution.
What is so conceptually difficult about this?
The fact that they were Catholic, and not Orthodox for longer after the Great Schism than they’ve been apart from her?
They may sincerely believe this, but this is the truth.