Body filler, the painter's assistant for good perceived value of the final product.

I agree any number of "fine" bicycle makers can be variable.

A finished bike will show the attention to the lugs prior to brazing and attention after. Overheating can sometimes be seen with the paint off depending on how the bike was prepped for painting. Obviously one cannot see this with the paint coat on. In general, if they bothered with the lugs they probably cared in the construction throughout.

The French are probably the poster child for showing poor workmanship but an effective frame. The Italians can go the other way, pretty where you can see it, maybe not elsewhere.

There are plenty of sound straight frames that show poorly on the outside, they will always be the last to get asked to dance but will make a pleasant partner when you get to know them.