As another poster pointed out to me, eminent domain is currently legal. Precourt is using all legal options available to him. Why shouldn't Columbus? AP will cry all the way to the bank so its not like he won't still get his cash. He's acting like an a-hole, negotiating in bad faith, and thumbing his nose at the city. Why shouldn't they drop that ED bomb on him? If nothing else, it can force both sides to negotiate in good faith.
"Just compensation" is the entire point of the debate around ED, along with "public use". The phrases are highly subject to abuse, and seizure based on one party's definition (the one with the power) is dubious in the best of circumstances.
Well, whether or not something is a good public use is decided by the public's representatives, ie city council or the county commission. The price he would get paid is subject to negotiation or a trial if no agreement is reached. If it did go to trial we'd get the comical prospect of Precourt telling the jury how great a market Columbus is and how the team is so valuable here.