Unless MacGill is using character in a very general way (which he may be, and in fact probably is, but I can't be sure), for me it's not about 'character' so much as 'how good they were when they played'.
Critical thinking is seen as a good thing, right? Without sounding overly preachy or whatever that word is, the method of critical thinking, basically, is to break **** down to their components and then compare those components, to find out what actually matters and what doesn't. So let's use critical thinking:
#1- You used the Hawks as an example, but they have in fact won a championship, which makes me think that not even you, defending this, truly believe the argument as JB framed it. A 'franchise that has never won before' is not actually the important part of that.
#2- You talked about cultures of teams, winning vs losing, and I reiterate that I mentioned the Wizards and the Jazz. The Wizards have won in the past and the Jazz have not, but I don't think any basketball observer would posit that the Wizards have a culture of winning where the Jazz do not. If anything, it's the other way around. So I propose that's a second piece of evidence that JB's 'franchise that has never won before' is not actually important at all- certainly not as important as he's implying- and actually, as I mentioned, rather arbitrary.
#3- So now let's investigate winning cultures and losing cultures and how players can effect it. Well, I propose that the best- and possibly only, let's be honest- way that they can effect it is by playing well. Play well enough, for long enough and the team is going to be better and the culture can slowly change. I think that would be a strong piece of evidence to suggest- breaking down the argument into components, being critical thinkers- that the more important thing that just 'changing culture' would be simply playing well.
#4- Why? Because a player that plays very well for a significant period of time in a winning culture is being unfairly penalized for something totally outside of their control as opposed to a player that plays just as well in a losing culture over a period of time to change that culture. Why would we allow that as observers? And how could we possibly objectify that subjective narrative? McGrady got a Magic team to the playoffs that sucked, and Kobe won a championship with Shaq on the Lakers. Is McGrady suddenly better now? Or, because the Magic had already reached the Finals- albeit with an entirely different team- the 'culture' wasn't bad enough to counteract his bad team? How does any of that make sense anyway: just compared the players on how they play!
#5- I think the conclusion is that we can accept that the vast majority of what JB is saying is just narrative. It means nothing. It is literally meaningless for most of what people, when they try to judge and rate and compare basketball players, are trying to do. It's arbitrary and ultimately pointless; it's a distraction that should be discarded.