I wish there was more data on the "from scratch" bit. I just cannot believe that companies are willing to let experienced devs who know your system and have proven that they can ship just walk out the door with all that value simply because you won't pay them more. It is a ubiquitous problem and my bosses have shared this view. My current firm is the only place that has proactively increased compensation, and guess what, the other ICs I started with six years ago are still with the team.