Valuncuinas is not enough of an upgrade over Zeller to warrant the package you've proposed. He does some things better to be sure, but other things worse. Definitely not the threat Zeller is with the mid-range jumper, for instance.
Especially since there's only one year left on his rookie deal, and extensions will be very difficult to negotiate this summer due to cap craziness next summer, this could very well be for a player who spends a single year in Boston. If you took Olynyk out of the deal, and depending upon the protections on the 1st, it's more reasonable.