3900x series are the most reliable consoles, I would not say it's a myth. It's my main console since 8 years. It has read tons of burned games, scratched games, and the combinations of those two. I bought it used already, and from the looks of it it has been used a lot before me. It still had the warranty sticker on it when I bought it, so it still has it's original KHS-400C laser in it from 2002(?). Since then I gave it a deep clean and also cleaned the laser, but god me alone I put 1000s of hours in it and it still works like new, reads every type of discs as of today. 5000x consoles that I have are working fine as well, but one of them gave me headaches already.
On the other hand, I would consider 7xxxx slim consoles to be the worst PS2 consoles you can get. One of them scratched up my discs, and one of them wouldn't read any other disc type than single-layer PS2 games before I got them repaired. Also, they get kind of hot after a time.
So long story short, I have almost every model of PS2s you can get and I tried them all, but I look at my 39004 as an absolute TANK, so I would recommend getting that model or an 5000x.