New growth is genetically engineered to grow quickly, in dense conditions, to have short branches & to drop branches quickly. Loggers have optimized for growing tree trunks, not trees. The wood quality is very different from these trees. They are sick. The wood from them is going to warp on you.
I suspect that wood density, tree health, warping of lumber, and the resulting new ingresses of water could all be correlated. I'd love to know more if anyone knows more details.
Your suspicion is incorrect. Warping happens as wood dries due to uneven drying and stresses in the wood. Old growth can be just as stressed as new wood - those stresses arise from winds, growing on a steep grade, etc. And old wood can be incorrectly dried just as new timber can be. The wood will not warp further after it is milled into a 2x4, kiln-dried and installed in a building. It may expand and contract due to humidity changes, but those changes will be minimal within a sealed wall. Timber found in a Home Depot is more warped than wood 50 years ago because of cost-cutting at the kiln and the use of much smaller trees for the mass market.
Water penetration into a building is 100% down to the exterior cladding and waterproofing system, it has absolutely nothing to do with the material used for the skeleton of the building. Cladding is done with traditional plywood, which is infinitely better than old-growth diagonal planking used a century ago. Waterproofing is via plastic wraps like HouseWrap or more recently the Zip system where the waterproofing is integral with the sheathing.
Houses today may be less durable than houses 100 years ago (although there's huge survivorship bias in that claim), but if they are it will come down to tract houses being built to a very low standard of workmanship. It has nothing to do with old-growth versus new-growth timber.
I live in a country where stone houses are the traditional norm and wood frame houses are still seen as flimsy despite becoming increasingly popular for new family homes.
The way I understand it, a major difference between the two construction styles is that stone is wet and wood is dry.
Stone shouldn't be sealed (hence the notion that stone walls can't be painted) because this traps the humidity and erods the stone. A major downside of this is that this means stone houses are more prone to trapping humidity, especially with better insulation, and grow mold.
Wood on the other hand must be sealed so you can use forms of insulation that are highly efficient but very susceptible to damage from humidity. A major downside of this is that the outer layers essentially act as a water barrier and even things like driving a dowel into an exterior wall can cause damage over time from water entering the wall via condensation on the screw.
Traditional wood frame construction in my country used wooden beams along with loam or stone. Because these buildings often expose wood to the elements and are generally wet because of the stone and loam there is an inherent risk of the wood decaying over time and I've seen restorations that removed almost everything but the wood frame to remove integral beams. There are many very old wood and loam/stone buildings left in my area but there are probably many more that had to be either torn down or stripped down to the bones for restoration.
I suspect that wood density, tree health, warping of lumber, and the resulting new ingresses of water could all be correlated. I'd love to know more if anyone knows more details.