The Blues' defense is essentially the same group that allowed a tiny 1.89 goals a game last season, so there's no reason to not expect more of the same.
Did the Blues go for the big free agent defenseman to play with Alex Pietrangelo? No. This offseason wasn't one that GM Doug Armstrong could work his magic with free agents. As he mentions to Jeremy Rutherford, many GMs were waiting for the CBA to be passed before figuring out if they needed to unload big contracts, so making a trade was difficult. The CBA and the general market of overpayment tied Armstrong's hands, which means that Pietrangelo might be on the first pairing with... Kris Russell? Is this something Ken Hitchcock approves of? Yep:
"I think Kris has settled into the type of player he’s going to be from an NHL standpoint," Hitchcock said. "He’s going to be a mobile, strong-defending defenseman that can get you points at times, but we don’t need to rely on his points for us to do well because he kills penalties, plays against good players, which he did in the playoffs (last season against Los Angeles). And he’s a really, really smart player with great defensive vision.
"I think it’s really calmed him down, too, not having to live up to the burden of what he did in juniors …it’s allowed him to be a player now, which is really good for him."