Even if this was a miscalculation by Daniel Sedin it's a miscalculation by someone who, at the time, had zero front office experience in the NHL.
Besides that is not entirely true there were already many warning signs on OEL in terms of declining performance, foot speed, etc. I brought this issue up during the time the trade was made many many here just scoffed at it saying stuff like "what does the media know" or "analyst don't know anything". I think many here just choose to believe the narrative Benning (and I guess Daniel Sedin) sold to the fanbase instead of people outside the organization who had a more objective view on the matter.
I remember discussing last year how the media is already talking about buying out OEL in the future as a problem and people said "oh look at the media making stuff up blah blah blah OEL is still a good dman that's just a LITTLE overpaid".