Regarding welding or brazing temperature and the feel of a frame’s stiffness, no hard facts but there was one Carlsbad Masi that was on the rack at the shop I worked for that just did not sell. I owned one and swapped wheels into it and test rode it rode it for an evaluation. It felt “dead” as if any power was just swallowed by the frame and never to be retrieved. Only one mind you, but was weird. Was eventually sold at a discount to a customer who more than likely just hung it up to display and boast. Who knows why.

many years later in a materials and processes class, there was presentation of time at temperature while joining, max temperature and rate of cooling, ambient air, the general temp of the space and various quenching approaches, oil, water and rate.
I thought back about that dead feeling bike.