The lack of mitering tube ends is more the method of larger high volume producers where saving 5 minutes per joint would really add up to a huge time savings after a few thousand frames. For a small short run or singular frame shop that savings has less value and could cost some reputation.

Perhaps the best known example of the savings that a well engineered joint (and joining process) can have is Trek. When they were still making their frames here in the US they began to use a one piece headtube and lugs form. A sheet of steel is stamped/cut, pierced and, wrapped then welded. Tange offered this part, among others. The head tube's "lug" were stamped relief, only the top and down tubes actually entered a socket. Those tubes were left square cut. Not only time savings from no mitering but also had less brazing filler in a far simpler joint to flow. Now add preheating stations on the frame brazing carousel and the time to flow the joint comes down to only a few minutes each joint. Andy