Probably true, but there are more wrong ways to weld any kind of seam, butt or flanged, then there are right ways. I'll speak out for flanged welds, they take far less time, and when a customer is already whining about how much the work costs, it becomes a real dilemma. I've seen butt welds crack, sometimes from grinding, sometimes from the shop trying to make the seam disappear and the weld is just a tad cold. Not everyone has a TIG and endless time to butt weld everything. There are proper and improper ways to do both types of seams, the procedure is far more important then the type of weld.

Using a good weld-thru primer on a flange weld, grinding the excess weld away (again, most of us only have a MIG welder), a good epoxy primer followed by quality seam sealer on the inside of the weld will for the most part prevent a flange weld from bleeding.

IMO, it's kind of like using filler. In a perfect world we wouldn't use filler, with labor prices as high as they are not everyone can afford the extra time and money to do all their body work without using filler.

JMO, I'm not a professional, just a practical hot rodder.