Any ultralight rifle should be limited to 250 meter shots. The thin, light barrels are prone to gross loss of accuracy due to harmonics and vibration, temperature stress and bedding mechanics.
The longer barrel theory is also incorrect. Anyone who has shot in competition, knows that the longer the bullet spends in the barrel, the more accuracy is lost due to jacket deformation.
The minute gains of velocity that a longer barrel may provide, only amounts to a few feet per second, but the effects of friction, vibration and bed mechanics, effect bullet flight to a far greater degree.
I agree on limiting range with ultralight rifle. I hunt in forested areas not subject to longer ranges. In target shooting the ultralight barrel heats up very fast after a few shots, but for my use its perfect on normally one shot kills.
Good points on long barrels, although noting that the Mil Sniper models seem to have somewhat long barrels, also undersatnding that a true sniper rifle will have the most precise machine work and bedding which should reduce the long barrel “play” you mentioned.