You're not wrong.

Marner and the Leafs have had their fair share out adversity, but man have they ever turned on him. Sad to see.

Marner is in his somewhat the same situation as Eichel. No good team has the cap for him without dismantling their team in order to fit in a 11m. And poor teams with cap aren't willing to give up much cause they can spend 11m better on UFAs.
I floated the idea last summer than the Leafs would be better if Leafs exposed 11m Marner and Seattle claimed him.
Taylor Hall and Zack Hyman signed for 12m.
Would the Leafs have been better having 13.5m in cap without Marner and the signed Ritchie, and signing Hall and Hyman?

I see your point although I would contest there are some important distinctions between the Eichel/Marner situations.

Eichel is injured and there is dispute about his value/ medical timeline. They really missed their window to trade him this summer.
Marner may just be getting traded for a "shake up"/ retool (If the Leafs can't break through this year)

Exposing Marner would have been a horrible route in my opinion. Not only would it be an indefensible move from an optics perspective, but it would be a bad one in reality.
Marner still has a ton of value, you'd just have to make a deal in the summer with some big salary coming back.