You probably won't see many level top tube frames MARKETED/SOLD as gravel bikes, but I don't think there are that many level top tube frames on the market anyway. My commuter has a slightly sloping top tube, was sold as a hybrid when new, has cantis, clearance for 38mm tires, gravel/cross geometry, etc. I think I could call it a gravel bike if I wanted to, but I don't do "gravel rides" aside from an occasional 1 mile stretch of a gravel road on my commute, which my bike handles admirably. In other words, if a frame works for a certain purpose, isn't it whatever you make it to be?
