This is true. It's complicated. Also, if you're too good, some people above you may feel threatened and they can absolutely destroy your career. It's total bullshit that people at the top want to pay it forward. They don't necessarily. They want to help people who remind them of themselves or a lesser version. They often don't want to help someone who might be better than them in any way.
If the incentives are wrong, ya. At the lower levels of big tech, I don't think this is an issue. Or maybe I've been fortunate but all my managers and skip managers seem aligned on helping progress my career. Maybe because we're not competing for the same position and there's room for growth. If slots are limited and you're competing.. I can see this though.
Everything seems to be easier inside big tech.
In most tech companies, it's dog-eat-dog, people are even using the code they produce as a tool for lock-in, negotiation and manipulation... It's like they believe they will never get another similar opportunity in their lives and are trying to hang on to power like a dictator or sometimes a mafia boss. It's not even about money or growth. I've seen this same dog-eat-dog behavior in a crypto company which grew from $0 to $4 billion in a couple of years. It was like everyone was trying to backstab each other and the machinations behind the scenes were incomprehensible.
In big tech, it sounds like people are holding the door for each other like "you go first, no, you go first."