Many claim that diesels have higher maintenance cost and are complex as though gassers are foolproof with zero mechanical issues.
While I can agree diesels have become more complex, gasser are not immune from complexity. Maintenance cost are basically a wash.
When it comes to towing the equation becomes do you want the most economical method/tool or do you want the tool that delivers the better performance.
If your goal is to save $$$ at purchase time a gasser will always win, If performance is your goal a diesel will come out on top.
Keep in mind gasser savings is significant when you originally buy, but there is minimal savings from that point forward, once you begin to tow with your truck.