I think evaluating retaining or moving on from Mullin at this time is less about what he's done to date and more what the short and long term prospects look like.
I don't buy the incremental year over year improvement angle, especially when you look at conference performances. But the reality is they did make the Tournament in Year 4, and others have noted strong attendance, fundraising, etc.
Given all of that, if staff and roster looked stable for next year + recruiting had been and continues to look strong? I doubt there would be much discussion. Which indicates this is more about projecting than just assessing the last 4 years.
And that projection is understandably challenging at the moment. Ponds - who committed to SJU in Fall 2015 - is the only U.S. high school recruit to average even 10ppg for this staff. That's how non-existent the high school recruiting has been for almost 4 years now, and it doesn't look promising for that to change next year. We just had one of the most talented starting lineups this program has had in 20 years, and couldn't surround it with a basic supporting cast to take the jump that first 5 was likely capable of. The recruiting just hasn't been there at anywhere near the level it needs be to compete higher in this conference and nationally. While program improvement isn't typically a straight line, next year currently looks less promising than this one largely as a result of subpar recruiting.
The entire staff is to blame for that, and it doesn't matter much to me whether that's Matt not having enough help, Matt not doing a comprehensive enough job, or some combination. It's unsatisfactory performance that likely needs fundamental change to both staff composition and approach beyond just hiring Matt's replacement.
The market dictates value. One way to look at this staff is, if all were suddenly free agents, would they be sought after for a similar role with another program? Matt, no matter how limited the skillset, has bona fide market value to recruit for other power conference programs, and is probably the only of last year's coaches you can say that definitively about. Would think Mitch is incredibly unlikely to draw interest as a full time assistant in a power conference. GSJ? I suppose it's possible given his dad's background and that he now has experience at SJU, but certainly not a lock he'd land a high-major assistant gig, might have to take a small step back.
Mullin? I doubt he'd be a candidate at places like VT, Alabama, Arkansas, etc. Maybe a place like Nevada closer to CA? I get that there might not be any other job he'd want besides this one which is great, but it would still be nice if he was doing such a quality job here that it was clear he'd at least generate interest for comparable positions. Don't think that is the case.
And that's a ridiculously challenging place for SJU and a new AD to be in. This is an SJU-specific opportunity that is unlikely to work anywhere else, if it can work at all. It has gone okay to this point, but doesn't look to be on a continued incline. And I think that is where the decision is.