[eloisant]

Most developers working on products, not just at FAANG, can be replaced but it's very costly.

You need to find a developer in the specific niche he was competent. Not easy because there is a shortage of developers. Then he needs to get up to speed with the stack and the processes used in the company.

So in theory yes, engineers can be replaced. In practice it's costly, with no guarantee of getting the same productivity, and the process to find someone will leave you with one person less for many months. When you have competent engineers that you want to keep, the last thing to do is to play the "I don't need you anyway" card.