One major issue people miss is, teams who give up prime assets, almost always do so, with the intention of extending the player acquired.
I'm not sure about this narrative. The retention rate is low historically. Since 2014, 1st round rentals to be re-signed: Eaves, Kane, Pageau (T&S), Zajac+Palmieri, Lindholm (T&S), Horvat and Gavrikov. Those that walked: Miller, Franson, Vermette, Sekera, Ladd, Hanzal, Shattenkirk, Nash, Stastny, Duchene, Hayes, Foligno, Savard, Chiarot, Giroux, Copp, Bertuzzi, Orlov, O'Reilly and Tarasenko. That's 7 for 27 (~26%). I find it hard to believe that GMs are unaware of that, when a trade of that magnitude is made. If the intention is not likely, is it really the intention or is it justification to make them feel better about the likely outcome (disappointment)?