Hard to know, and the hindsight bias makes it even harder.
He was a pretty highly regarded prospect with defensive issues at SS, was called up and had a decent first 150 PAs in MLB. His second season was not so promising (80 PAs.)
I think the trade was more about ridding themselves of a pitcher they could not rely on, while saving some money. They and I thought Grissom had a decent chance at winning the 2B job and maybe sticking close to his .746 OPS with the Braves. Again, "maybe" he could even be okay on defense if playing just 2B.
We had sucked at 2B for a while. We had gotten next to nothing from a $26M pitcher for years. I see how pissed posters get over $21M for Buehler, $19M for Sandoval and $10M each for Kluber and Richards, because of us ignoring their injuries and injury histories.
Sure, none except Kluber were ex-Cy Young pitcher, and I get the apples to oranges aspect of my point, but the fact was and still is, Sale was fully unreliable at the time we traded him.
Sure, we shouldn't have had to pay $17M, too, but the deal made some sense at the time. That doesn't change the results, and the results were the trade sucked, but I still think there was logic to it.