Mig welding has it's place......It's fast and good. Tig welding is slower and great. I have as much money in my spool gun's and mig welder's as I do my tig machines. They are faster and you can do good welds with them if you practice.
I did a job about three years ago
click I did the design, fabrication and installation of this piece. Each ring is 30 foot in diameter and composed of 250 pieces of aluminum. So each side of each ring is about a 100' of welding just on the exterior. Now each side had to be triple passed. So that is 300' per side per ring...... 1200' worth of welding. When you start talking about that much welding you have to do it quickly or you will go out of business.
My point is, each welding process has it's place. I would tig weld aluminum all day long. It's my favorite process and metal....But it is faster to mig weld it if your set up for it.