I don't think the concern about being the villain is really dictating his actions.
At some point I think we have to take into account that money is a real factor here. Johnson is not a sure-fire NHL talent. While burning a year of his ELC is nice, the reality is that he is going be be earning AHL ELC wages, so something like 60 - 70k. (I will admit that I am not up to date on what AHL ELC wages are, someone please correct me if I am way off.)
If he lands on a team and gets some time as a #7 D even, he's propably looking at 800-900k. So he has to look around the league and assess where he has the best chance of that happening.
Maybe he develops into an NHL regular, and then the money and contract issues will resolve themselves. But if he doesn't, a few years making 900k sure beats 3 or 4 years in the AHL earning one-tenth that before maybe finding a gig in another league.
Does Buffalo offer a good path for him? I think that is likely his dilemma.
I was joking about the villain thing (I was just trying offer the obligatory pessimism)
But I do believe Johnson is pretty much a sure fire NHLer. Whether he's only a 3rd pairing guy or anything more than that, that is up for debate and requires time to tell.
So if it is about the money, then him signing here and burning a year off his ELC by getting a few games in this year would be very appealing to him.
But if his heart is in California (like Adam Fox's heart was in Manhattan), then he'll go to UFA or perhaps request a trade there, and we can flip him to LA or ANA for a 2023 2nd.
Whatever the case, we'll find out soon enough.