I am part of the extremes when it comes to properly fitting production bikes and even I recognize that there are plenty of options I could choose from.
Having a short torso is hardly reason to declare production road bikes dont fit you, seeing as how a Lynskey GR300 frame fits you fine.

GR300 geometry-
S - 550mm stack and 375mm reach
M - 570mm stack and 380mm reach
L - 615mm stack and 390mm reach
XL - 635mm stack and 400mm reach

This type of geometry can be found on countless road bikes. Heck, there are plenty of endurance road bikes that will have even less aggressive stack/reach numbers.

As for if a road bike will be faster than your gravel bike- thats been answered, but history shows repeating helps solidify the correct answer so...
- If your position is the same and you have the same equipment on both, you really wont be any faster on your road bike.
- If you have faster rolling tires and your position and equipment are the same, then you will be slightly faster on your road bike.
And in the end, your road bike may feel faster simply because some geometry is different- HTA, Chainstay length, trail number, wheelbase, etc all impact how fast a bike feels. You might be the same speed, but it feels faster because of geometry differences.

Based on your comments in your gravel frame thread and how you set up your old Colnago road bike, I really suggest you work with a bike fitter to understand geometry and how various changes in bike angles impact fitment.
There will be a ton of bog common road bikes available that will meet your fitment needs, based on the fact that you fit a stock GR300 frame.