from the looks of it there is a crack already formed in the rust. and $50 says if you open the hood there is rust in the other side too. meaning it went right through.
Not to mention if you grind away the rust to find clean metal, your taking 16ga or less sheetmetal down to much less. And you never get all the rust out fo the pits in the metal, and chemical rust removal/sealant is not allways the best.
cut remove tack grind fill paint.