The GS payscale is not set up to be able to hire and retain highly skilled technical experts. Even if I were to be hired at the GS-15 level, I'd take a pay cut from what I earn as a contractor.
I once worked on a contract in a Systems Engineering and Technical Assistance (SETA) capacity, which was both an odd and eye-opening experience - basically advising the govt customer, as a technical expert, on contractors' proposals and sitting in on reviews and such.
That's a good fallback option, though it's still difficult to control turnover and feel like you are aligned in terms of value using that approach. You'd want to find somebody that you trust and bring them on in that special capacity, rather than just putting an RFP on the street for a SETA advisor.
Agreed on the GS payscale and its ability to keep up with high-end private sector pay though I also think that the entire hiring process may be more of a barrier than the pay itself.
All that said, a non-supervisory GS-15 in the DC area (18% locality pay bump - more if you're SF or NY) is maxed out in the 170s which isn't shabby!!
When you combine that wage with generous retirement matching options, job security, good work/life balance, and excellent health insurance at well negotiated rates it ends up being a pretty attractive offer.
Furthermore, there are other government agencies and roles that have their own specialized payscale outside of the GS scale. This can include financial regulators (higher pay to avoid revolving door problems) as well as "cybersecurity" billets across different places.
I once worked on a contract in a Systems Engineering and Technical Assistance (SETA) capacity, which was both an odd and eye-opening experience - basically advising the govt customer, as a technical expert, on contractors' proposals and sitting in on reviews and such.