I live for the CABE
LOL, your both correct, but it gets confusing.I always understood that the whole point of brazing a frame is that it's less heat than welding. Any high carbon steel can get hard if it's heated enough, and as a general rule the harder something is the more brittle it is, so hardening is good for cutting tools and wearing surfaces, but not good for frames. Welding works well on low carbon steel because low carbon steel doesn't get hard, but it's not as strong as high carbon steel.
On the other hand I think the Super Sports and Sports Tourist frames from the '70's were silver soldered instead of brazed, so maybe even brazing was too much heat. The only welding I had was an introductory course many years ago, so there's a lot I don't know. But I read somewhere that "silver solder" is actually mostly nickel, the name comes from "German silver", an old name for nickel. If somebody on here knows more about this, don't hesitate to enlighten me.
Welding (gas, or electric like MIG or TIG) joins the steel metal by melting the steel at a high temperature and adding a filler rod. Welding is best used for joining thicker materials, let's say 1/8" or thicker. Because of the high temperature required it's a pretty aggressive means to an end but produces a very strong joint.
Brazing joins metals at a lower temperature using Brass/Bronze as the filler and a flux to make it flow. The metal does not need to be brought up to a steel melting temperature for the filler rod to melt. Since the Brass/Bronze filler rod is a soft material it serves well in sanding/grinding to make the smooth transition of the Filet brazed joint. The down side is that it is "very easy" to undercut the filet brazed joint when finishing the brass joint area and grind/cut into the metal tube reducing the wall thickness. Schwinn Chicago had occasional problems with this issue. Some of the "hand made" BMX STINGS, and the Giant produced mountain bikes had "undercutting" issues on filet brazed frames. Giant sent a team of inspectors to each of the four Regional Distribution Centers to sonic test their frames to determine which had to be replaced before they were released for shipment to the dealers. I'd bet the filet brazed frames @cyclingday had problems with were frames that got "undercut" at the factory.
Lugged frames have the advantage of using the lowest temperature of all three frame joining methods. The low temperature allows the use of very thin wall frame tubes, and the joint is done "almost like" sweat soldering a copper water pipe, but of course on chrome moly steel it is done with silver solder. Because the joint is done at a lower temperature it also makes it easier to replace a frame tube for a repair.