However, I do have to point out that it seems that Epic is trying to become more competitive with regard to that same subset of engineers that Google hires. Presumably, if they're trying to become more competitive, then they're not yet competitive. Either Epic will have to pay some engineers the same as what Google pays (including equity etc.) or they won't remain competitive for that small pool of devs.
Also, worth noting that I'm saying that as someone that was once rejected by Google on a first-round phone screen.
At that time, they were not offering salaries that were even competitive with other companies in Madison. Never mind about Seattle or SV. I had four managers in 2.25 years, because three of them left for higher pay elsewhere almost as soon as they got promoted. I left the fourth for ~20% higher pay.
I would guess that any major tech employer could stroll into town and hire the best 50% from under Epic's feet in less than two weeks, while still saving money on salaries compared to SV. Queen Judy is not taking that company public, and would rather divert her profits to charity than to employees. There won't be options or RSUs. The only reason people might stick around is the cult-like atmosphere.
It might be the case that salaries won't become truly bimodal. It seems like there might be "tiers" of compensation which are based on levels of competition between similar companies. SV startups tend to pay less than Google or FB, but their compensation packages are typically within the same ballpark of each other. Perhaps the bimodality is most notable for new grads, since they typically don't get hired at mid/small companies.