We got Hayward, why would we need Butler or George? seems kind of silly in retrospect to get mad Ainge traded for Irving because we could've gotten redundant guys.
Irving is not really a lateral move from Thomas. Thomas really peaked last season, got injured at the end (which will likely be the end of his prime), and we saw his defense fall off a cliff. It was clear Thomas was no longer going to be the same and not to the tune of 9 figures.
Although Irving seems like an equivalent talent at the moment, he is 3 years younger, putting up his best season last year with Lebron and Kevin Love on the same team. It means he has another gear, the same gear we saw in the playoffs. It means he can get better, improve not only his offense but his defense. He has a great supporting cast that he didn't have when he was first leading the Cavs before Lebron showed up. Brown and Smart are going to protect him like Bradley and Smart did last year for Thomas. Hayward will should some of the offensive and creating workload to make it hard for teams to isolate Irving on an island. Horford to help orchestrate the offense and do the little things. Morris to defend and score in a pinch. A strong bench led by Tatum and Rozier. And not to forget our Head Coach Brad Stevens, who will work his magic.
This team finally has a limited its weaknesses to one single flaw: interior rebounding. And as Ainge's first big three taught us, you don't need to have the best rebounding if you make a lot more of your shots. The Celtics didn't need to wait to unload these assets because they found a guy that will solidify contending for this upcoming season and the foreseeable future.