21 years of experience certainly helps. I don't disagree that Argon/CO2 mixes can be better, but for home use, the cost far outweighs the small benefits. Mig isn't the best suited for anything less than 1mm thick. I've welded cars and sheet metal < 1mm thick but have to spot it to avoid overheating, but that's generally the case no matter what gas you use. Nowadays, I use my TIG set if I'm working with sheet metals or need better pool control. Welding rusty, galvanized or painted metal is bad practice. Preparation is everything. But you already know that.