If Westbrook were on a longterm deal, or was willing to sign an extension as part of the agreement, one would have to consider it. However heading into free agency, it's a risk.
Porzingis is one of the best young talents in the league. At this point the smartest thing to do with him is let him be for a few years, up until year 5 of his NBA career. You'll have a really clear picture by then of what his real value to a team is.
To be honest, when Porzingis plays well, his value is more than Westbrook. He can give you 2nd option offense and on the other end board, defend. If he gets more consistent over the coming years, I think he'll be one of the 10 most valuable players in the league, even if he's not putting up monster stats like Westbrook.