I'm with Cellar-door. I'm fine with him playing 50-60, as I was willing to accept the possibility that Smart gets hurt and only plays 60 given what he added to the team. I'm willing to accept the possibility that Porzingis has a down-year offensively. But what Porzingis does bring to the table - a seven footer who knows how to protect the rim an defend the pick and roll - is just more valuable to me than Smart's free-safety stuff. And if the offensive improvement is real, than the upside for this deal is positively enormous.
That said, I'm not even really as excited about his offense or the upside as I am about plugging the gaping hole at center we had (yes, yes, prom night). At the end of the day I think they're both winning basketball players, only the Celtics needed a center badly and already had four point guards, one of who is admittedly not rotation quality in Pritchard (notwithstanding the comparison I made to FVV a couple years ago, which I have got deserving shit for ever since), but two of who are starting caliber in Brogdon and White.
I don't think Porzingis guarantees us a championship. I'm not assuming that he will be 100% healthy. I think if he's on the floor, the value he adds will more than cover for the loss of Marcus. Will we miss him? Sure. But we all wanted insurance against TL coming apart at the joints and Horford aging, and in order to do that, we had to give something up. It sucks, but them is the breaks.
It was my perception that Smart had lost a step, and my fear that heading into his 30's those injuries might accumulate or he might lose a step or his intensity on defense. That perception/fear might be incorrect. Perhaps he ages like Chris Paul - still effective defensively but missing chunks of time here and there. Or Tony Allen for that matter. Good for him, if so! Regardless, I think Porzingis is not only a better fit for this roster but exactly the sort of thing we needed.