To be clear, the Sunday & Feast Day lectionary repeats on a three year cycle and covers essential teaching** but not the full bible (<50% of NT)**
Year A: Gospel of Matthew
Year B: Gospel of Mark
Year C: Gospel of Luke
John is used on Easter, Lent & Christmas
If you attend weekly, listen earnestly, and ponder the teachings thoughout the week, then you will know alot about the Bible.and be a spiritual Christian.
However, if you attend less frequently, are are easily distracted, and don’t revisit the Sunday lesson throughout the week, then you won’t know much about the bible and are not feeding your faith
To put a twist on this, can someone be a spiritual Catholic without studying the Catechism? Many essential points are not covered in regular Mass.
Personally, I’d put regular study of the Catechism above reading the Bible since it has distilled the essential Scripture and teachings of the ECF. That will juice up your spirit.
There is a huge difference between attending mass, and going through the motions vs really learning doctrine.