I think the issues are not just how DIA performs, but also the ecosystem in which it operates in.
To begin with, there is a fundamental flaw in DIA only being concerned with the artificial boundaries of "Downtown" and not taking a more holistic view of how to engage the larger metro area in connecting with Downtown. It basically acts as if Downtown is apart from the rest of NE Florida and I think that is a big mistake. Sometimes, I think it should be specialized division of the Planning Department if we could find a way to keep it out from under the thumbs of the politicos in City Hall.
Examples of better integration would include better transit connectivity with the surrounding urban core and, addressing another issue, stronger coordination with Public Works, FDOT, JTA and the NFTPO. The Emerald Trail (which I don't even see DIA as being a leader on) is a step in the right direction but it is just a toe in the water to what should be done.
Making the boundaries of Downtown more seamless would likely also help to overcome the psychological impediments many area residents have about "going Downtown."
DIA should be better integrated with other facets of the City such as cultural institutions, Visit Jacksonville, the Jax Historical Society, the hotel and restaurant associations, parks, nonprofits, community organizers, neighborhood associations and others (beyond just the Jaguars and money hungry developers). And, as stated above, it needs to better connect dots with other agencies at the local, state and Federal levels.
Most importantly, DIA needs to show the community a clear vision/plan for Downtown that reflects wide community inputs (not just what its staff and consultants think are best), be more disciplined about sticking to such a plan over a long period of time and not fawn over the developer rendering/project of the day. If developers don't comply with the master plan, we need to say "sorry" and move on. In support of this, there needs to be best-in-class downtown zoning regarding street engagement and aesthetics, green spaces, setbacks, height restrictions, architecture, scale, historic preservation, etc., not some random walk with developers.
We also need to say that we will incentivize developers by investing in community infrastructure that supports their project rather than "investing" directly into the project. This would not only benefit the developers but the entire community and, hopefully, leverage such investments to support further development in the area (i,e, a multiplier effect) creating some real momentum. The lone exception is incentives for historic structures and such incentives should be based on either multiple contractor bids shared with DIA or a 3rd party audit of the single bid contractor.
The DIA board needs to be more diverse, and maybe enlarged, and include people not just tied to development, construction or real estate, but also representative of business owners, residents, nonprofits, environmentalists, historians, accountants, financial analysts, etc. Members should be representative of being a Jax resident for from 5 years to decades. Terms should be staggered so that people are going to be selected by more than one mayor/city council over time, insuring the board isn't reflecting one mayor/city council's "philosophy" over downtown.
The above may not be all that should be addressed but it would be a good start.