What are the cons of exclusively pumping breast milk and feeding baby using bottle versus breast feeding?

Efficency. It's more efficient to breast feed than to pump & then bottle feed. You also avoid any risk of less than perfectly sterile bottles causing the milk to carry an infection. In addition, baby's nursing tends to trigger you to produce more milk than pumping. That said, having breast fed both my kids, pumping when i was away & nursing when i was with baby was a very effective compromise.