Well as the big bass said of the fluorescent lime green plastic worm it had just swallowed: "I just didn't want to see something like that get started in the lake". We feel that way about completely bogus assumptions about quality or tradition.
People may get called out on, say, lugs if they say something implying that other build methods are inferior in some way. Or if they say "given I am going to the Andes and need the strongest frame possible (or one with radically novel geometry), therefore it has to be a lugged frame... We just want to be helpful. But if they say they like the way they look well who can argue with that (OK I have found ways but enough with the details for now).
The original claim in your post was that pinning is a classic tradition, which is one way to characterize nailing, I guess. I'm going to have to mention that to my framing friends, like maybe we need a t-shirt or something. Actually timber framing is another art that has elevated the insertion of a wooden pin into a joint as something akin to fitting the sound post in a violin.
"i worked as a certified pressure vessel welder for many years and think there's a reasonable rationale for the use of pinning such as:"
You must have gone through a lot of lugs and pins in that trade...
"-having only to heat the tube once per lug and therefore a reduced chance of overheating, & distortion of the materials,"
What you want to find is a guy with a zero chance of doing either whether he is using pins or hanging from the ceiling in a tutu. That's the real classic tradition, learning to do it right regardless of what it takes. The stuff that doesn't show in your nail bag. I'd rather find a guy who can be trusted not to set the bike on fire regardless of how he is stabilizing his joint.
- that pinning removes an inherently 'dirty' step in assembly which could potentially introduce impurities and porosities during the final brazing operation
It isn't inherently dirty, as you point out, it can be successfully done one way or another. It's all using enough flux and temp control.
- that pinning allows for more easily adjusting of tube alignment during the assembly process
Who cares how easy it is? The whole thing about being a pro is that everything is easy for you, as in the phrase "he makes it look easy".
-and that pinning offers the possibility of lower stresses to be built into the frame as the structure is joined.
Well that is certainly one way to describe driving an oversized pin into an undersized hole in a casting.Hey, I want to go firmly on record as one of those people who doesn't care what criterion you use to select your frame builder. Just so long as a new mythology doesn't get started.