We already know how the Cs are with him so it doesn't really matter if he goes on to make the Nets worse. By signing him to a max contract, his value would have remained similar to what it is now and we would have been able to trade him for a significant return had we remained stagnant - which we wouldn't have if we added AD. And, while that assumed improvement should be more attributed to AD than Kyrie, Kyrie still gets to reap the benefits of being a 'leader' on a successful team.