> I don't know if Lego is getting weaker
Yes, the new Lego is definitely more brittle than than the old, and also less capable of dealing with tensile stress. I have a couple of examples of very recent bricks that spontaneously broke along a side wall simply by being stacked on other bricks.
The first formulation (Cellulose-Acetate) tends to deform and warp, the first generation ABS bricks are as good as indestructible unless you use main force.
At the moment Lego produces both in Denmark and in various locations around the world and there is a real difference in quality between batches from different locations.
You can also tell by holding up bricks to the light, the more transparent ones (relative to other bricks of the same density and color, best to test with yellow, white and red) are the weaker ones.