I believe much of the "Sig quality slipped" came from some teething problems with the Mosquito early on and the run of P220 stainless that had weak extractors, with a healthy dose of "Americans suck and Germans are little precision machines."
My Sig P220 has been flawless, and I wouldn't hesitate to buy another Sig handgun.
When SIG first came out with the polymer guns, they had some teething problems (2022, P250). Also when they switched some of their production to the U.S. rather than Germany quality slipped for a year or two.
I've only owned older SIG's (220,225 and now a 228) and never had problems with them. I am seriously looking at a 227 to replace the 220 I foolishly sold!