I agree with you, except I think Grigson was terrible. Yes, he did have some nice draft picks here and there and he had a few good moves (trading for Vontae Davis or signing Mathew Adams etc.), but as you mentioned, the list of mistakes he made.... Richardson was just the icing on the cake. From drafting Dorsett to signing Andre Johnson, Arthur Jones, RJF, Akeem Hicks, good gosh. Even those, who were okay (Trent Cole, Redding) were overpaid etc. And personality is part of the job 'cause it affects relations to other GM's and of course affects the locker room, so him being a jerk made him even worse GM. I't still baffling that he was GM of the year in 2012, but that was Luck I guess. Yeah he didn't miss on Luck with the very first pick, bravo.
Ballard is the polar opposite as GM. Personality wise as well as how he's operating. He isn't perfect of course. Nobody is. He makes his mistakes. But all in all, the number of mistakes compared to the good moves he has done is not even in the same ballpark where Grigson was. Ballard is one of the best in his position, and I think, by now, this is practically a consensus (judged by 5-6 years, not just one having the 1/1 pick and a Luck coming out of the dradt).
Regarding game changing free agents, I'm not sure honestly. True game changing talents won't become free agents often. You have to trade for them. Look at the WR position for example. Who were the top 10 free agent wide receivers last year? Kenny Golladay, Curtis Samuel, Corey Davis, Nelson Agholor, T.Y., Juju, A.J. Green, Marvin Jones, Emmanuel Sanders, Kendrick Bourne. This year it is Christian Kirk, Allen Robinson, Valdes-Scantling, Russell Gage, D.J. Chark, Zaj Jones and Julio and Landry will join them soon. Is there a game changing name amongst them, in the current state of their carreer? Even Allen Robinson. I wanted him in Colts uniform ever since he left the Jaguars, no doubt that he is uber talented but ... is he even a top20 in his position? He's been in the league for 8 years now, he had only 3 seasons when he played all 16 games, he had only 3 1000 yard seasons. That's not #1 numbers.
Yeah, of course, he can be "that last piece". But in my book being "that last piece" not equals "game changer". That last piece can be a veteran Emmanuel Sanders or a clutch kicker if he land at the right time at the right place. But that's a different thing. When it comes to "game changing free agent" I expect excellency, I expect leadership, I expect elite-ish production. And I expect it for years, not for one playoff run etc. That's a game changer free agent. And I think this kind of free agent is very rare. Teams have way too many ways to manage their cap situation so they keep their game changers most of the time. And if they don't, they want to trade them instead of just letting them be free agents.