The Colt design has proven itself to be more than adequate for over 170 years. What else has withstood such a test of time?
Here are some of the results of my own research. The Army changed over to Remington during the last few months of the war not because the design was superior, but rather due to the fact that they were offered at a much cheaper price than the Colts. And they had plenty of problems with the new pistols, including burst barrels and cylinders, sight orifices being drilled straight through into the bore, slag left on the frames and the Remington's Achilles heel--the cylinder pin would foul up after only a few shots. After the war, Remingtons were dispatched to the troops out West, and General C.C. Augur, commanding the Department of the Platte, wrote to his superiors regarding the pistols: "Defects of the Remington pistols are as follows. They are made of very poor materials as shown by the great number burst at ordinary exercise; in some companies 10 or 12 burst in one year. Capt. Ball took 3 of them out for trial with ordinary charges and all three burst at the trial. The springs are not strong enough to burst the caps, and in many of them the hammer is not long enough to reach the cap... At a firing drill on the 27th, 40 pistols were loaded carefully, and out of 240 loads, not more than 150 could be discharged at all. All of this has so disgusted the Company commanders here that they prefer to have no pistols at all; they consider them almost a usless weight for the men to carry. On the whole, I think if it were left to Company commanders, they would not take them into the field... The Cavalry should by all means have revolvers and these should of course be reliable. Colts have never to my knowledge been found fault with in any important particular, [but] if Colts cannot be supplied, [than only] Remingtons which have been thoroughly tested and found to be perfect should be sent to replace those found defective..."
In other words, you get what you pay for. Shortly after, Remington lost favor (and orders) with the Army, with most in stores being sold as surplus to the European market. In London, many were sold off for as little as eight shillings apiece.
The Army did believe that the top strap made the pistols more rugged, true or not, and required any new pistols submitted for trials be fitted with this design. It was this requirement, rather than any defect with the open-top design, that prompted Colt to add the top strap to their pistols.