I seem to recall the fatter growth rings they put in on spring/summer increasing the density of the wood.

You could be right though, I'm having trouble finding it on Google tbh.

The main thing is that the wood quality is different because they want to maximize quantity over quality.

it's absolutely the other way. the dense rot resistant wood from older forests was basically mined away by companies, like wyerehauser and others, over the previous 3 centuries.

My 100-year-old house in British Columbia was built entirely of Douglas Fir. At this point, you can barely pound a nail into the studs and joists. The density is incredible. New lumber feels insubstantial in comparison.