False. Lego is some of the most precise injection molding in the world. The tolerances are insane and they nail them every time. Compare with offbrand building blocks and you'll feel the difference.
Micromolding is very hard, and Lego is the best at it.
10-20 years ago, sure. Nowadays you can get basically the same product from LEGO compatible competitors for way cheaper. Dunno how many modern sets of the variety of competitor stuff you've assembled recently, there's huge variance. Some of it definitely has crap QC. Some of it is really, really good now. My wife put together some knockoff 8000+ piece set the other year and the pieces were basically flawless.
Where I've seen the difference is in the quality of the instructions (which matters) and the packaging (which arguably doesn't). The bricks themselves are, as you say, basically flawless.
Exactly. I bought 3 or 4 China Lego clones to try and the parts were slightly different in size and in color. Some blocks way too big, so building was not good experience. For original Lego you don’t need sanding paper on the table.
Micromolding is very hard, and Lego is the best at it.