
The Oilers need to maximize Broberg's value, not trade him for the sake of a trade.
Philip Broberg is going to be a fantastic two-way defender in the NHL. The question right now is will that happen with the Edmonton Oilers or another organization?
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It's possible to trade for roster players without giving up your best defensive prospect. They need his inexpensive deal because of how close to the cap ceiling they are. Plus, if they trade him now they won't get as much as they could if they gave him more ice time and let his value rise.
With the re-signing of depth forward Derek Ryan the Oilers now have $5.07 million left in cap space. Evan Bouchard will more than likely sign a $4M bridge deal. That leaves just a shade over $1M for the Oilers to work with. The cap situation is very tight right now, which makes a trade (or several) a matter of when not if.

Broberg is still on his entry level contract (ELC), which is a good thing for the Oilers. They will need prospects and AHL players to step up and battle for NHL roster spots with whatever depth signings Ken Holland typically makes in free agency.
Who is left in the prospect pipeline on defence? Max Wanner, Cam Dineen and Markus Niemelainen are all good in their own right but if Broberg is gone there is no one close to having his level of offensive tools. It's necessary to give something of value in order to get something else valuable. That being said, the Oilers forward cupboard is more full and that should be where they take a prospect from to trade.
Broberg has only played between 12-13 minutes on average over the past two seasons with the Oilers. With only 11 points in 69 career games, they can't convince prospective buyers that he's an offensively gifted player. At best they could convince another team that he's a future 2nd pairing defender who just needs an opportunity.
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The better course of action would be to play him 17-18 minutes a night. Get him on the penalty kill paired up with Mattias Ekholm to mentor him. Watch his game grow and then sell high on him.

Ultimately you want to see a player your team drafted stay with the team. But if you are going to trade him, do it when his value is higher than it is right now.