Since that skill is odd but required by every single contractor that does classified work there's a whole lot of opportunity out there I wasn't aware of until recently. The lack of quality people doing it in the GS ranks now makes a whole lot more sense to me. Prior to me understanding that it was just an annoyance.
Also, DC Metro is an extremely high CoL area (not SF levels but probably around Seattle levels). Normal GS-15 pay is $112k-146k and you'd trend towards the bottom of that in most areas.
So, $112k average at the peak of your career, with a required Ph.D. More realistically as a new hire you might be GS-12 (which only takes a master's) which is $68k-89k, so you make $68k in most areas. That's certainly not great as far as competitiveness with tech salaries, that's pretty close to the bottom of the market these days for a new hire working entirely remote, not even highly-desirable talent.
My take-home in the first full year at work was $147,500. The second was $178,500.
Feel free to adjust for inflation.
It looks like it may be a little above L3 salary today (moving in the right direction!), but still far below L3 TC, and a Google L3 job is not even remotely comparable to a GS-15 job.
IMO if the government had a separate band of GS pay for highly competitive job markets which paid 50-100k more, they would be a lot more successful.