NASA's modern budget isn't eaten up by satellite and ISS maintenance, it's eaten up by pork/corruption like the SLS. The SLS was already largely obsoleted by the Falcon Heavy 7 years ago. And Starship will make it look like a 13inch black and white CRT (with a million dollar price tag) in the era of cheap 80" bendy flat screens. Artemis is a similar story. Artemis simply isn't going to work. The entire project is filled with unrealistic handwaving.
Yet NASA continues to cheerlead for these things. I briefly thought NASA might right their heading under Bridenstine but then at some point he suddenly just did a hard 180. It seems every man has his price. He eventually just turned into another Boeing cheerleader (and his new found rubber stampage is a big part of why that Boeing monstrosity left astronauts stranded on the ISS) and went straight from out of office to a high level advisory gig for some MIC company which is almost certainly just a laundered paycheck.
Obviously percentage of GDP isn't an ideal multiplier for reasons you've mentioned, but then inflation indexed mainly to mass produced common consumer goods tends to significantly underestimate the increase in cost over time of running complex operations involving the world's smartest and most on-demand minds and an almost unfathomably large number of subcontractors. Either way, NASA's overall budget is half that of the 1960s in regular inflation adjusted dollars, and whilst its current research and satellite/ISS maintenance maybe aren't as exciting as the first lunar landing, they're not obviously dramatically lower cost (the %GDP argument gets brought up nearly as often to suggest the Apollo programme wasn't worth it...)
Sat in a lecture theatre with NASA's last chief economist using both metrics earlier this week. Although those slides were looking at cumulative funds spent on Robert Goddard's programme, which was about the size of a largish Series A using the inflation metric or Series B using the GDP adjustment. Whether that's value for money or not depends on whether you're considering being the father of modern rocketry more impressive than sending a handful of moderately complex 16U Cubesats or rideshares or note that the actual rockets were no more sophisticated than some student projects, I guess...