nope.
your statement would apply, I agree, if all things were =.
That is a false assumption in this case.
Bruins made him available b'c they had a surplus and needed the cap space, that's the bottom line.
They sent him to NY, not to punish him, but b'c they didn't want to send him to a contender, esp in conference, but he may not have wanted to go west, so they compromised with NY.
The above means it was not an open market, which again, has real fact that there is league wide shortage of quality RDs, and esp more so as to availability.
Plus, yeah, this is a rental this year only, but that also means no long term commitments. Sometimes you prefer term, sometimes not, depending on the player and circumstances.
2nd is doable and somebody will pay
ESPECIALLY if there is injury, and there usually is
further exacerbating supply and demand