A packet line is defined as a regularly scheduled cargo trade back and forth between ports. If there were no packet lines between the southern ports and Europe then that's an indication that the amount of traffic between the two destinations wasn't enough to justify a regular schedule. Which would indicate the volume of imports just wasn't there.
Someone ignorant of the numbers of ships involved in trade, what routes were profitable, and the amount of goods being transported via coastal ships and railroads might think that there is some valid conclusion somewhere in your question.
But of course you are not that ignorant.
Why don't you just disclose what you want to prove or disprove.