If Sleiman is so concerned about low rents being a factor in getting deals done without these fees, why doesn't he take the stance that developers literally everywhere else now take? That is "make it more difficult for others to compete with me". Whether that means fees, excessive zoning regulation, red tape, winning the lottery to become one of a city's few developers, $1M/SF land prices (usually driven up by other HIGH barriers to entry, not low), etc.
The reason developers outside of Sleiman, a few apartment builders riding the current wave, and some homebuilders, aren't looking at Jacksonville is because they'll get killed in the first year. Too cyclical, too much inventory to fill still, too probable that someone else will build a mirror image next door, no oversight, no protection, etc.
This is why "developer" in Jacksonville has come to mean something so vitriolic - people don't even realize that "developers" are often interesting hometown heroes elsewhere with their number one vice being their big egos to build the biggest and best things for their respective cities.
Granted it is true that in most places the suburbs offer the biggest yield for new development. Making the switch is a difficult one. The payoff is potentially a lot more, though. I think developers in Jacksonville like Sleiman are worried that the city will never be able to figure out all the ingredients necessary to build inward instead of outward (i.e. the multitude of ingredients necessary to launch infill development, including but not limited to having the audience, which requires a whole other set of parameters the city doesn't have yet), and so any regulation forcing that inward development or restricting outward development becomes pointless in the grand scheme and ends up a money loser for those developers. Again - no faith in city leadership and for good reason.