Could you do/ have some stem and bar swapping to get the hand position closer?
One of the fundamental differences between a gravel bike and a 90s MTB (other than faster rolling, larger diameter,tubeless tyres made from decent rubber and light but strong carcasses, and hydraulic brakes, and wide range, close ratio drivetrains and modern frame materials, and availability of brand new bikes, rather than 30yr old NOS bikes) is that the difference in bar position (and width) that gives a much more aerodynamic position on the bike which makes them quicker or easier to ride over long distances and on typically less technical terrain 🙂 (see also the lack of hybrid bikes in the TdF).