Is Derrick Rose the player he used to be?
No, but that doesn't mean he can't still be a piece to the puzzle for the Knicks. What we have to remember here is that Carmelo Anthony is under contract for the next three years (the last is a player option). He is currently 32 years old and still playing to an all star level. The Knicks cannot afford to be patient with the remaining prime years of Anthony's career and rebuild around young talent. If they want to do that, then somehow they have to persuade Anthony to waive his no trade clause, and if they can't do that he is going nowhere. Thus, the Knicks need to be aggressive in building a play off caliber team around Anthony and Porzingis. While Rose is no longer the all star, he is still capable of contributing in a supporting role.
Did they have an alternative to Rose in free agency?
The main PG free agents are Mike Conley, Rajon Rondo, Jeremy Lin, Deron Williams, Brandon Jennings, Ty Lawson, Matthew Dellavedova, Raymond Felton, and Mario Chalmers. Being totally honest the only one worth pursuing would be Mike Conley because he would give the Knicks an excellent defensive player, a capable scorer, and a decent play maker. But outside of defense where Conley beats Rose, there wasn't very much between them in stats. Rose beat Conley in PPG and FG%. Conley beat Rose in APG and 3P%. So there is an argument that if Rose can stay healthy, perhaps he can boost his assist numbers, and become more efficient since he's still getting over three major injuries. Granted there is a risk he doesn't get over them, but think of it this way, Rose has one year left on his contract to prove he deserves another contract at the end of it. If he bounces back and has a strong season, the Knicks will try to extend him. If he fails, the Knicks will let him walk. It's a one year loan and all they had to give up was an average players in Robin Lopez, Jerian Grant and Jose Calderon. In return they got a former all star in Rose, plus a player and a second round pick. I think that's a good deal.
Could they have built through the draft?
Well, not this year since they don't own a first or second round pick. So unless they manage to acquire a draft pick, they won't pick in this year's draft, and that means no drafted young talent to support their existing team. Ok, they own their first round pick in 2017, but with growth from Porzingis, Anthony playing to his usual level, and any production from their supporting cast could play them out of a difference maker in the draft unless they won the lottery. So in a sense, the only way they could build through the draft around Porzingis would be to persuade Anthony to waive his no trade clause and get assets for him in return. Based on what Anthony has said, he has no intention of waiving that no trade clause and is going nowhere. So unfortunately this type of deal, combined with free agency and other trades, is the way the Knicks are going to improve.
Don't get me wrong, I agree that Rose is inefficient and a shadow of his former self. But he doesn't need to be the all star he was, he just needs to stay healthy and become more efficient. Put him in the starting line up with Anthony and Porzingis and they have a decent trio to build around. All they need to do is sort the SG and C positions, and fill out the bench and they'll be a play off team next season. With players opting out they should have cap space to sign people, and while we may question Rose's current ability, there is no question that some free agents will view the Knicks with Rose, Anthony and Porzingis as an attractive option in free agency. And that's without considering the market size and off court opportunities.