"If a modern gun company were to make one today and use the steels that they have available today, the break top design would be just fine, and could be used in all but the most powerful shells available."
I don't think so. The problem is that the top break MUST have play at the top joint in order for it to open. And every time the gun is fired, that play allows the two parts to batter each other. Not a lot, of course, and careful workmanship will minimize the gap and the battering, but IT WILL BE THERE - it cannot be eliminated.
Revolvers like the old military Webleys gave good service because their cartridges, while large in caliber, were of remarkably low pressure (which is why those Webley revolvers converted to use .45 ACP should NOT be fired with standard .45 ACP loads). The same was true of the S&W revolvers. An S&W No.3 latch would not last long if fired with ammunition at .44 Magnum or even .45 ACP pressures, assuming the cylinder stood up to that punishment. I have seen loose No.3's, indicating that they did not really even stand up well to extensive firing with the black powder ammunition of the day.