IT had an absolutely off the charts single season last season. He was the primary scorer on a team that did not have much other scoring, was highly efficient, and the team won. IT was very good in the playoffs until his hip flared up so you can't really "yeah but" on him about the playoffs.
Kyrie has had a run of several excellent seasons and playoffs but it is hard to say that any single season was better than IT had last season. So if you think that IT is going to continue to play as well as he did last season for say 3-5 more seasons, then I think it is hard to argue that Irving is any better. If you think that Irving is about to blossom and make a leap (much like IT did around that age), then OK, Kyrie is the man.
I think more realistically, Kyrie is going to continue at his current high level, maybe with some improvement and IT is probably not going to repeat last season. I do think that IT is going to continue to be better than people think is possible for a 5'-9" guard with a bad hip. Both players are going to do well and both teams are going to be able to claim victory with the trade.