If weight reduction is the main object, the realistic options IMHO are carbon (maximum frame and fork weight savings), titanium (typically <1800g/4lbs, customs are reasonable from Waltly, if you understand frame design and can read a drawing), or in steel something like a custom from Rob English. The last wouldn't be cheap, but should be pretty wonderful; check out Rob's Instagram.
Steel disc forks are going to be way heavier than the carbon equivalents, and I wouldn't expect suppleness. This can be overcome with a Shockstop stem. Steel *rim brake* forks can get down to ~700g/1.5lbs, but not disc forks due to the different loading.
Bear in mind also that gravel-ish frames typically include lots of mounting points and are expected to be able to carry stuff, whereas road frames are not. Their weight is thus necessarily greater.
Non-custom frames have to be strong (and stiff) enough to ward off complaints about excessive flex, and to reduce or eliminate warranty claims, limiting how light and/or flexy they can be made.
Later,
Stephen (who might eventually end up with a Trek Checkpoint SL5)