Not really. The Suns' defense was much better at the start of the season, and I don't think that Bledsoe can take full credit. Hornacek is still doing a solid job, but the bloom is off the over-achieving rose. It's true that this roster isn't built to play half-court defense or get quality shots when the game slows down -- but earlier in the season, they were getting it done in spite of the roster limitations, and that was what was so remarkable. Now they look like pretty much what you'd expect from an undersized team with a bunch of undisciplined shooter-athletes.
I think they look like pretty much what you'd expect from a team missing one of their two best players. There are a few teams that can lose arguably their best player and not miss a beat but most teams are far more vulnerable than that. And since losing Bledsoe we've been a very mediocre team. We've chalked up some big wins but even bad teams do that on occasion.
I don't think the bloom is really off the rose though. Prior to the season we expected to be bad and now, even without Bledsoe, we're playing like a middle of the pack team. We're still overachieving we're just not overachieving to the degree we were early in the season. On paper we certainly don't look like we're only 6 points weaker than the Warriors or that we're capable of sweeping Indiana.
Losing Bledsoe hurt us on both ends of the court. But you're right, his absence isn't the sole reason our defense is struggling. We were showing a decline on defense even when Eric was still in the lineup. It's much worse now but the decline had already started. We benefitted from a decent early season schedule and the fact these guys could play without the burden of expectations. We probably also won more than a game or two because other teams had difficulty taking us seriously once they got a look at our roster. But I still think losing Bledsoe is the single biggest factor in our decline.