I think it's different things that are acting on the hood to make it seem more or less rigid.

Propped up, there is less structure of the hood to keep it's shape. But that's offset force from a passenger prop, gravity, etc.

BUT in place, the advantage of the (frankly enormous) trackspec vents is that there is SO much pass-through area that even though the structure of the hood is somewhat weakened by cutting it up and installing the vents, there is SO much less surface area of the hood to catch air and make it flop/wave in the wind that it actually appears stronger when driving.

ZERO experimentation - just something I noticed with a friend's car with the trackspec vents. It does feel floppier in the hand but seems to barely even get hit with air/wind under movement. Doesn't mean it's stronger, but the result is that it's less effected by the wind.