I think you need to decide if you want a flatbar or dropbar bike. You can call it gravel, or whatever you want. By 'fitness' bikes, that seems to be hybrid frames (same geo as the lower end ones) but with skinnier tires, a carbon fork and a 2x crank. Either style should give you much more relaxed geometry than your road bikes and significant advantages to riding your hardtails.
Both styles (hybrid and gravel) should give you plenty of clearance to add fatter tires. If you're travelling around into the unknowns, I think it's best to prepare for the 'worst' (roughest) trails you'll ride. Don't get any front suspension. I take it you're not riding super steep trails, but a 1x or 2x configuration will give you the needed min/max gears. But 1x drivetrains do have larger jumps between gears. Consider the biggest tires needed and the gearing needed, I think you'll find options in both styles.
Personally, if I'm riding more than three hours I want dropbars for the variety of hand positions.
And it doesn't matter what style of bike you ride, you can wear lycra with a flatbar or baggy shorts and shirt on a dropbar bike. I used to go full lycra on MTBs, but now I'm sometimes wearing baggy shorts, and the best thing I've discovered is to wear some loose Underarmour shirts instead of jerseys that cling to me and gain a couple of pounds of sweat. Only downside is no back pockets, but my baggy shorts hold a couple of gels and my backpack holds the rest if I'm MTBing. Break all conventional wisdom, do as you wish.