The massive downgrade on defense is not worth the upgrade from Toffoli to Nylander. Calgary was a fish out of water last year when Tanev got hurt. Weegar helps fix that depth issue but doesn't negate it entirely. If Tanev is traded and then one of the top 4 gets hurt it's the exact same boat

There is no way the Leafs are trading a young Sandin and potential top pairing defenceman for the often injured and older Tanev or a more skilled Nylander for Taffoli.

This is exactly the type of trade Toronto needs to make to get over the hump. They get a player who will be an asset in the play offs on the blue line and a forward who can score in the important play off games and won't run from the first sign of contact. For someone who is considered a potential top pairing defenceman, Toronto won't even pay him 2 million per year, and have him sitting behind 2 defensemen whose best years are in the rear view mirror. Doesn't exactly scream top pairing defenceman from the team that should know him the best.

Weegar is not depth, he is a Top 2 D-Man

He is but you miss the point. Lets say Tanev gets traded and then any of Weegar, Hanifin, or Ras get injured. Then Calgary is stuck with the same issue as last playoffs.

Im not calling Weegar depth, Im calling Calgary's defense depth bad if they go down 2 top 4 defensemen (1 via trade and the other injury)