Biggest misconception is one is stronger than the other, they are not. Biggest problem faced is lack of fusion with tig if you see the puddle not fuse you just hit it with the torch and fuse it. With mig it is a little harder to ensure complete fusion. Sequencing your weld also plays a big factor. Both have their advantages and drawbacks.
I'm not sure if this turned into a dick measuring contest, but it sure feels that way. I'm not trying to tell you or anyone else how to weld. As a matter of fact I don't really know much about welding. Never claimed I did.
A few people have trusted me and I guess I've done ok by them.
If you feel better migging cast to mild steel by all means go for it. I'm just doing what I was taught by an engineer who has been doing this since the early 70's and through trial and error has come up with this process.