Iberia will know if you miss your flight because you were slow at the airport. You won't like the outcome (or treatment) if an IB agent decides that you are responsible for missing your connection.

A recent data point. I was on a delayed BCN-MAD connecting to ORD. Because much of the plane was connecting, they diverted the plane to T4S. Not great for those on the Puente Aereo, but a sign that IB is often aware of what it needs to do with connecting passengers.