Of course not every book on my shelves is a masterpiece, but today is the comparative wasteland for Secret Projects-pertinent titles, not the 1990's.
I don't know if I would agree that "today is the comparative wasteland for Secret Projects-pertinent titles". Take Chris Gibson's stellar series on British projects for example:
Vulcan's Hammer: V-Force Projects and Weapons Since 1945 (2011)
Battle Flight: RAF Air Defence Projects and Weapons Since 1945 (2012)
Listening In: Electronic Intelligence Gathering since 1945 (2014)
Nimrod's Genesis: RAF Maritime Patrol Projects and Weapons Since 1945 (2015)
On Atlas' Shoulders: RAF Transport Aircraft Projects Since 1945 (2016)
Typhoon to Typhoon: RAF Air Support Projects and Weapons Since 1945 (2019)
They Also Serve: RAF Reconnaissance and Support Projects Since 1945 (2024)
Then there's Chris's (and others' - such as
Paul Martell-Mead's P.1103 and P.1121 book (2015) and
Mike Pryce's BAe P.1216: Supersonic ASTOVL fighter book (2011)!) equally excellent Project Tech books on Blue Envoy, such as his peerless series on British helicopter projects (with
James Jackson).
And of course
Tony Buttler's many projects-related books - too many to list here really.
Justo Miranda has published at least seven books on secret projects from 2014 to 2023, with more available as ebooks.
Dietmar Hermann, Robert Forsyth etc. have produced a number of German projects-related books recently.
There are regularly excellent secret projects-related articles - based on new research - in
The Aviation Historian magazine by various authors - particularly Professor
Keith Hayward.
Also consider the following:
The Secret Horsepower Race by Calum Douglas (2020)
Teach for the Sky: British Training Aircraft since 1945 by James Jackson (2021)
American Secret Projects 3: US Airlifters Since 1962 by Craig Caston and George Cox (2020)
French Secret Projects 1: Post War Fighters by JC Carbonel (2016)
French Secret Projects 2: Bombers, Patrol and Assault Aircraft: Cold War Bombers, Patrol and Assault Aircraft by JC Carbonel (2017)
French Secret Projects 3: French and European Spaceplane Designs 1964-1994 By JC Carbonel (2021)
Westland Aircraft & Rotorcraft: Secret Projects & Cutting-Edge Technology: Secret Projects and Cutting-Edge Technology by Jeremy Graham and Ron Smith (2024)
Boeing B-47 Stratojet and B-52 Stratofortress: Origins and Evolution by Scott Lowther (2021)
Lockheed SR-71 Blackbird Projects by Scott Lowther (2021)
US Supersonic Bomber Projects Vol 1 by Scott Lowther (2022)
US Supersonic Bomber Projects Vol 2 by Scott Lowther (2023)
American Interceptor: US Navy Convoy Fighter Projects by Jared A. Zichek (2022)
Supermarine Secret Projects Vol 1 - Flying Boats by Ralph Pegram (2022)
Supermarine Secret Projects Vol 2 - Fighters & Bombers by Ralph Pegram (2022)
English Electric Lightning Genesis and Projects by Tony Wilson (2021)
Hawker's Secret Projects: Cold War Aircraft That Never Flew by Christopher Budgen (2023)
I think Osprey's X-Planes series is up to about 16 volumes between 2016 and 2022 - including
Steve Richardson's ground-breaking work on the XP-67, to name just one.
I myself have put out maybe 17 or 18 Secret Projects-pertinent titles - all based on primary source research - over the last 8 years or so. Perhaps there were dozens more Secret Projects-pertinent titles published during the 1990s but I would say that we're still reasonably well served for such material today - at least 70 'secret projects' books released since 2010.
Maybe your argument is that these books aren't available as frequently in bricks and mortar book shops - I agree - but it's not difficult to purchase high quality secret projects-related books crammed with new information today if you want them.