I was under the impression that little in terms of welding technology has changed much, with exception of robotics being very consistent in quality and repeatability. That said, I was told by one maker that for their mass production steel frames, they were now getting cheaper tubing that was "super-butted" and pre-formed for their frames and this allowed them to butt weld simply because now the tubing at the joint was thicker. And the use of robots to do the welding made the work much faster, cheaper, and more precise than could be for average humans. So this reduced the HAZ issues that might migrate out of the super-butted region.

For aluminum, I think the extrusion technology has really been the key and we see curved frames and not straight tubes even with customized joint designs for frames because robots can TIG weld extremely well. I think that's what makes the biggest difference. In the old days of working in the machine shop building pressure vessels, I learned to TIG weld and stick weld and braze. And it wasn't easy to lay down a fine bead consistently, and every time I had to stop and itch something and took the inert gas off the bead and restart, it weakened the joint especially with aluminum. I think the real difference here is in robotics and automation of the process that has enable butt welds to achieve strength. They were always strong if done right, only humans were flawed and only a few could do it right consistently. Machines have changed that.