They aren't "waiting out a neighbor to fill in over the pike," they are the neighbor to fill in over the pike. That's in the next phase. And if they had put up a solid sound barrier, people on here would for sure complain about how the barrier shows that they aren't committed to the next phase.
Damned if you do, damned if you don't.
As someone who lives in the (West) Fenway and passes along this site to connect to Beacon, this project is a HUGE improvement for the neighborhood. That might not be so obvious on a "Pike drive-by," but it's very pronounced on foot. This corner used to be the deadest, saddest spot in the whole West Fens + Audubon Circle area. Now it is very far from that. I'm pretty psyched about it.
The cladding is lousy, sure. But the street levels (two of them!) are fantastic, it does a lot for non-auto modes (a new signalized crossing of Beacon!), the massing is great (I'd take this form over some cheap 5-over-1 any day), and the groundwork it lays for future improvements is unlike just about any other project I can think of in recent memory. Of course we all want developers to go all in on both cladding and street level design, but I'd much rather the developer skimp on cladding and invest on the street level than the opposite.