The open top design is not weak. And Colt had a top strap design 20 years before Remington.
The open top wasn't weak considering what it was designed to shoot. The top strap design was obviously superior in withstanding higher pressures from BP cartridges and later, smokeless powder cartridges. I doubt the idea for the top strap design was to make a more solid frame as much as it was to ease disassembly, but turns out it does make a stronger frame. Thanks to Colt, or whoever thought of it. As HisSOLDIER said, the top strap design has survived to this day and the open top is history. To argue this is to lie to yourself.