Meccano seems like a better choice for learning about mechanisms. (Sorry in advance if you're about to drop a few grand on those...)
The tolerances are far worse than with Lego, but there are many more possibilities to build workng machines.
I'm just reading a book about technic history with Fischertechnik, where all kinds of differentials, steering mechanisms, planetariums (yes, with several planets, ecliptic, and so on) and even several types of mechanical clocks are built.
Perhaps only by those "not in the know" so to speak. For the general consumer, yeah mostly.
But if you're into DIY robotics for any length of time (or perhaps other STEM pursuits), you likely know about it.
That said, Fischertechnik makes Lego look cost effective...
Dirk Fox, Thomas Püttmann ISBN: 978-3864902963