The Church not only preserved the OT, but made possible the NT. That is why the Church HAS to be thanked. Case closed.
The OT had been preserved in total 400 years despite the presence of the political structures that would have desired its extinction.
Made possible by the Catholic church? Christ Himself promised that it would be preserved. The thanks go to God. The Catholic church claims credit for the work of God. Matthew 24:35; Mark 13:31; Luke 21:33 It also claims extra-scriptural dogma is necessary for salvation so that claiming credit for God's work shouldn't and doesn't surprise anyone.
The church was founded on Scripture, not the way Roman Catholic twist it around.