That’s not what my post was insinuating at all. There are a few typing errors in my original post which maybe made it difficult to read. 55gr lead core bullets only need a 1/14 twist to stabilize, but that means they will be stable in any twist rate faster than that, which includes the common 1/9, 1/8, and 1/7. What I was saying is that if you use really cheap ammo with poorly balanced bullets (not perfectly uniform), a twist rate faster than what is needed exaggerates the imbalance and will cause degraded accuracy. The reason most classsic rifles have twist rates just fast enough to stabilize bullets they were designed to use is because bullet manufacturing was not very precise in the past. The slower twist rate lead to greater accuracy. Now days, bullets and manufacturing processes are much better, and in most cases it’s a non issue.
The 1/2x28” threading has nothing to do with bullet stability. It can cause the release of the bullet from the muzzle to be less consistent if bore swelling occurs. This is well known among barrel manufacturers. How much impact does it have on accuracy? That is unpredictable. Sometimes it has none, sometimes more, but it’s usually not a tremendous impact.