You'd be surprised! I have a few smaller Lego sets (and I have tons of spare from childhood), and the quality of some knockoffs is basically identical to the real deal. Trust me when I say the knockoffs have figured it out in 2023. The real differentiator comes in packaging and quality control. It's not uncommon for a set to have a few missing or incorrect bricks, which you need to order or replace from your own collection. In the end ABS is ABS and this molding tech is literally 50+ years old; there's nothing holy about Legos process.
If you do a quick search you'll also find tons of people complaining about sore thumbs and fingers, particularly after putting together large sets. There's plenty to flame the knockoffs about, but this ain't it
For the past two weeks it's been Legos. I always wanted to build big kits as a kid, but they're way way too expensive, even for me today now that I'm making decent money. Well lo and behold, there are tons of knockoff Lego manufacturers, many of whom will just sell you 100% ripped off sets for dirt cheap. I just put the final piece on the new Rivendell set today, and I'm going to start the millennium falcon UCS here soon. Unfortunately, it'll have to wait until my thumbs heal up from all the damage - placing tons of bricks really chews up the tips of your thumbs and index fingers