MIG welders are dangerous because people who do not know how to weld, stick things together with then and can't understand why they break. Anyone who actually knows how to weld can look at the pictures and see that they are FUBAR, The problem is hobbyists often CAN'T. classic example of insufficient penetration and trying to weld dirty material, or perhaps badly contaminated wire.
Certainly you can wire feed 1/4" plate; They wirefeed bridges and skyscrapers these days, BUT ther is a world of difference between dip transfer and spray transfer. You probably can't get spray transfer with such low amperages, so a novice often gets very weak low pen welds like we see in the pictures. The Miller he says he used is more than capable of welding the mount. HE is not, being a hobbyist. Nothing that can't be cured. of course. Anyone who owns a MIG welder should take some classes so they know how to use it correctly and know what it is capable of and NOT capable of.