The Sigma got a bad rap because of the so-called "agreement" that S&W foolishly signed
Well, there was that. There was also the design of the trigger return spring which required a felt wad inside the spring as a vibration dampener. When American Handgunner did their 10k "torture test" they "cleaned" and cooled the gun by dipping it in a bucket of water. (IIRC, it was water.) Somewhere along the way, the felt wad got displaced and the trigger return spring broke. I think this happened two or three times (a S&W representative was on site to observe the test and fixed the gun when it broke).
At any rate, gun owners being the panicky bunch they are didn't bother to figure out what actually happened. They read the executive summary and the Sigma's reputation took a hit. The fact that the design of the return spring was changed and the felt wad was no longer required (IIRC) was lost on everybody. (Honestly, the felt dampener seemed like a hack to me. As though the MEs at S&W knew the return spring was a problem.
If I had to guess, I'd say the part was already undergoing redesign when someone in management said "Hey, I know you said those new guns aren't ready and gave me a long, drawn out technical reason why, but we're demoing one tomorrow. I'll need it at noon." So, they cobbled together a workaround, but didn't take into account the gun being
rapidly heated (shot as fast as magazines could be loaded) and
rapidly cooled (dunked in water when it was too hot to hold) dozens of times over the course of an afternoon.)
This is all from memory and the latter part is speculation. I stand to be corrected.