You're confusing a language (the way people speak) and a literary tradition (the way people write).
When ancestors of Russians borrowed Church Slavonic writing, they were already speaking another Slavic language, Old East Slavic. For the time being, they were writing in one language (Church Slavonic) and speaking another language (Old East Slavic). Later, they dropped Church Slavonic and started writing what they spoke.
Modern Russian language is a continuation of Old East Slavic, not of Old Church Slavonic.
You're confusing a language (the way people speak) and a literary tradition (the way people write).
When ancestors of Russians borrowed Church Slavonic writing, they were already speaking another Slavic language, Old East Slavic. For the time being, they were writing in one language (Church Slavonic) and speaking another language (Old East Slavic). Later, they dropped Church Slavonic and started writing what they spoke.
Modern Russian language is a continuation of Old East Slavic, not of Old Church Slavonic.
This is the scholarly consensus.