There is/was lots of speculative armchairing as well, when HSLAs started coming into the picture. Structural adhesives also get pointed to as a reason not to do

There is/was lots of speculative armchairing as well, when HSLAs started coming into the picture. Structural adhesives also get pointed to as a reason not to do big repairs like this. In practice it isn't really borne out. HSLA (high strength low alloy) steels are stronger (and therefore lighter) than mild steels. Many alloy steels (non-HSLA) are sensitive to heat treatment and improper welds make them weaker, so tons of people were being very vocal about HSLAs ruining cars, making repairs impossible, etc etc. Things like saying you'd need proprietary filler to match the composition, that welds would be poison, etc. In reality it doesn't really make a difference. Adhesives are also sometimes/often used to secure panels together instead of welds. The theory was that subtle differences in shape would introduce tensile stressed that would cause adhesives to pop in a crash. Not real. Alternatively stress during modifications could introduce cracks and weaken the adhesive- also bullshit, those adhesives go through stress every time they drive. They're fine. They aren't invalid concerns, but unless you're putting a torch to the adhesive or welding seams down the middle of alloy beams, you aren't doing anything that will cause problems.