Yeah...this. Some teams search for years for a 1D. You don't trade a 20 years old 1D unless you have a REALLY good reason to. We have every reason to believe Severson will be a star and none of our other D will likely be as good. You can't just name a bunch of our young D prospects and call them 'depth' just because there's a lot of them. Anway depth only means something if you have a star at the top.
Drouin IS a really good reason to. I'm not advocating trading Severson but Drouin is going to be an top line talent. And you use Severson and star way to loosely. Severson has looked fantastic but thats all based of a 40 game or so sample size. Severson isn't exactly the next Weber yet. You are ridiciously underrating Drouin. Its not fair to put Severson on a pedestal and simeoustaneoly talk of Drouin as if he is on the prospect level of Reid Boucher. And quite honstely the way this team has been drafting it could take years before they draft a top forward talent thats not a top 10 pick.
The Devils do have defensive depth. The sheer quantity of quality prospects in the D pipeline is bound to produce at least 3 or 4 NHL defenseman. Add on the success the organizatin has had in the 2nd round (Gelinas, Merrill, Severson) and hopefully Santini and Jacobs.