This is a load of baloney. If it was welded before, it can be welded again. You only need to heat the effected zone not the whole frame. Also put a sleeve over top and add more weld. Heat treat isn’t anything fancy. Get a temp gun and a propane torch. Get it to temp and let it cool slowly or quickly or both. depending on the spec you find.
The only reason they cook the whole frame is because it’s easier from a manufacturing point of of view.
Amen.