The very first sentence in the study footnotes:
1 The authors did not attempt to estimate how much of the reported local investment and spending would have occurred anyway in other parts of central Ohio had the Arena District not been developed.
Most economic impact studies are simply tools created to sell someone on something and small print footnote disclaimers such as this are the reason why they aren't worth the paper they're written on.
Really have to disagree here. The AD economic impact can be measured because it exists. Had it never been built, there was no guarantee anything of equal value would've been created elsewhere in the city. Trying to disregard current value because it may or may not have come in another form could be applied to literally every single last development, from the suburbs to the urban core. I'd take established value over the nebulous "might've been" any day.