This is a troll thread, right?
It's not that complicated.
Gravel = drop bar, usually with a rigid fork but sometimes small travel suspension. Frame geometry generally ranges from "road race" to "XC". Tire clearance is more limited. If you put a flat bar on a gravel bike, it's a XC MTB.
XC = flat bar, usually with a suspension fork but not always. Geometry on hardtails is basically identical to slack gravel bikes, but some XC bikes have full suspension. Tire clearance is generous. If you put a drop bar on a XC bike, it's a gravel bike.
A drop bar is beneficial because it's more aero and offers multiple hand positions for long stretches of cruising straight roads. The downside (compared to flat bars) is that drop bars are generally lower, the flat part is narrower so they are less maneuverable for technical terrain. Also the levers are on the drops. If you want more maneuverability for technical terrain and don't care about longer stretches where aero or ergonomics might matter, then flat bars are great.