No, when you're thinking in terms of phylogeny, feathers do NOT a bird made. Neither does a wishbone (which almost all theropods had), a beak, a partially fused hand, etc. Since many of these features evolved prior to the origin point of Aves (including feathers, which may be very ancient), it's only when so many of these features "build up" in a single lineage that you can call it a bird.
For example, let's take pygostyles...shortened tails. Birds have them. But so do oviraptors, which are clearly not birds. But wait, oviraptors had feathers, too, and beaks, and wishbones. So why aren't they birds? Well, they can't fly and their immediate ancestors couldn't fly either, so they're not like ostriches. But they nested like modern ground-dwelling birds and slept like them, too, with their head underneath a wing.
However, because we have so many good fossils now (far more than we had in 1993), we can see where birds actually split off from other carnivorous dinosaurs. If you climb the phylogenetic tree past oviraptors, there's a big split between Aves and Deinonychosauria. They share a common ancestor (it probably looked a lot like Mahakala), but both groups share many features in common. The difference is that Aves continued to modify their wings and bodies for flight, while Deinonychosauria actually lost many of those features, possibly because of competition from Aves, and were forced out of the trees.
There is some validity to the idea of pushing the term "Aves" down one node to encompass all birds AND Deinonychosaurs, since both initially have flight adaptations. So at a certain point, where you label something a bird or not is arbitrary. It's very hard sometimes to tell, when you get right down to the point of common ancestry, which one is a bird and which one isn't.
However, I imagine that if you saw an Anchiornis sitting in a tree today, we'd call it a bird even though it couldn't fly very well. It was about the size of a raven and had just as many feathers, if not more (it had "hindwings"), and its feathers were colored like a modern hairy woodpecker.
So in a sense, "Aves" is in the eye of the beholder!
Honestly? My short answer is that it's not a bird if it can't use true flapping flight. I don't think the Deinonychosaurs could, but you know what? Neither could many early birds! Archaeopteryx, Confuciusornis, and others seem unable to complete a flapping stroke. I'd actually suggesting moving "Aves" to the crown-group (all living birds and their immediate ancestors) and calling stem-birds something different.