You bring up several important talks, so let me try to do my best to address them and separate them with answers worth of the question.
In talking with agents and players and free-agent players in recent years, I can tell you that the hacking scandal has come up precisely ZERO times when it comes to why players don't sign with the Cardinals. It just hasn't been a factor at all. Maybe it has with the public perception, and it's certainly made the Cardinals an easier target for Cubs fans, but it has not been a factor or part of the conversation at all when it comes to free agents or trades. The only time a no-trade clause has been invoked against a deal to the Cardinals in recent years was Stanton, and that was telegraphed: The four teams he said he'd accept a trade to were the four teams in the ALCS and NLCS the previous year and two of them happened to be the biggest-spenders in the biggest media markets, Yankees and Dodgers. Shocker. What worked against the Cardinals in that case was geography -- and not being in the playoffs the previous year.
I don't know of any comments that Jason Heyward made that were that specific, not in the way you imply. Perhaps you could share a link to them or quote them? He did speak in general terms about the Chicago atmosphere, and that he was drawn the clubhouse there and saw it as a contrast to the clubhouse he experienced with the Cardinals. No kidding. One clubhouse had Joe Maddon as manager and penguins, and the Cardinals had Mike Matheny as manager and he and the influential players set a different tone. I remember in 2016, there was a report -- based loosely on Twitter -- that Heyward heard racist taunting from the stands at Busch Stadium. The toxic words were allegedly picked up on the ESPN broadcast. I went through the entire game again as did the people at ESPN, with the sound enhanced, and there was no evidence of it, and Heyward the next day said that he didn't hear any during that game. But ... but ... he added that he has heard it in the past and learned to ignore it at ballparks that he declined to identify. He said ballparks, as in plural. Which should alarm all of us.
It was after the 2016 season that Dexter Fowler signed with the Cardinals. He was coming off of a World Series win with the Cubs and Heyward, and he was the top free-agent leadoff hitter available. Yes, the Cardinals upped their offer with a year beyond what other suitors -- like Toronto -- were offering, and it's worth noting that Fowler spoke with Ozzie Smith about his decision to come here. The protests in Ferguson and the perception of St. Louis were questions he and other free agents have asked the Cardinals about, and they have had to be ready for answers. Coming out of 2020, those conversations are rightfully going on throughout the leagues.