The compensation bands and the actual compensation are exactly the same regardless of immigration status.

Bands yes, packets no.

Big tech companies aren't like a Government job with rigorous pay grades based on role and seniority. You can have people even within the same role and level at big tech with multiple $100k pay discrepancies.

If someone's continued ability to stay in the country where they currently live is contingent on employment then they will accept worse conditions and pay.

That's the entire reason why tech companies use H1B, it's not as though there's a dearth of Java developers or DevOps people who are US citizens.