And for comparison's sake, here is the setup at Ralph Wilson Stadium, which is surrounded by parking lots, versus the current layout of the inner harbor, at the same scale:
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Keep in mind that a chunk of that land below Bear Street is already slated for development. You'd need a plot of land twice the size of what is currently there if you want to avoid having to surround the stadium with parking garages instead of lots.
Inner harbor is Slated for smaller scale development though with traditional framing.
One thing to consider about the inner harbor is that Foundations is a huge problem/cost for a building this size with a large clearspanning roof, ie Domes, compounded with concentrated load areas, ie stadium seating/concourses.
For reference Destiny sits on a huge number of 220ft+ long steel piles because of how bad the soil is and it is semi-traditional steel framing. They actually lost some piles completely by just hitting them once with the Pile driver the soil down there is so soft. Can be very expensive.
It becomes a mat foundation with a raft of piles for clear spanning roof structures though they would be shorter piles the further you get from the lake as bedrock rises, lets say 150 ft long for the stadium.
More technical stuff (read at your discretion)
Carousel sits on a compensating pumped water content bathtub foundation that is constantly tracked and adjusted and columns are adjusted annually to level it out. Out of the question in this case in my opinion.
The soil near the dome has pretty good capacity in comparison, and while it may need short +/-20-30ft friction piles due to high loads and mediocre bed rock at certain locations, spread footings are an option in lightly loaded areas. Overall either system is a big invisible cost savings over the inner harbor.
The site down on east Fayette from what I have heard is some where in the middle in terms of soil, (thanks retro, if I recall correctly) sounded to me like +/-40-50 ft piles would be needed in most areas. They may have considered this worth the cost of investment to reclaim campus adjacent property for academics under the previous scheme especially with the state kicking in.