Useless poorly informed discussion on Eurosport regarding road bike or time trial bike frames for a mountain time trial.
When you go uphill at 25 km average, aerodynamics only play a minor role. Seat position (back), open hip angle, and bike weight are far more critical than aerodynamics. And a bull horn bar will give same upper body/hip angles as standard drop road bar, but only very slightly more aero. Where possible above 30km/h you'd be on the aero bars anyhow, not the drops or bull horns.
So best uphill bike frame would combine backward seat position ( ie flat seat post angle) and low frame weight ( ie usually road bike frame). And of course aero bar extensions.
If the mechanic can be bothered putting bull horns on the road bike frame that would be better than road bars, but would require recabling, so usually not done for the one brief ride.
Gear changes either via the usual combined brake/gear shifters. Or, via a re-cabling, at the ends of the aero bar extensions. Hardly worth the hassle of re-cabling at a low average speed of 25km/h.
So standard road bike with a simple aero bar extension on the road drops the best solution overall.