Andersen is 1000x better than Not-so-big-save Dave. Your giving up an elite starting goalie, top 6 forward, middle 6 forward, high B prospect to get an elite LW and a downgraded goalie. Then you trade the elite LW to get a top 4 D and a blue-chip prospect but end up giving up the blue-chipper too.

All in all a huge L for Toronto

No. We likely won't be able to hold onto Andersen after next year anyways and Rittich comes with a small contract. I consider that trade off about equal. We also give up Kapanen, who although is quite good will never be better then Nylander or Marner and is a perennial 3rd liner and Johnsson who is essentially a cap dump for us for Pesce, a top-pairing shutdown defense men we 100% need. Losing SDA doesn't really matter given how many forward prospects we have. Basically, the trade is 2 3rd liners and a mediocre prospect for a 1RHD on a great contract for 5 more years.

they're giving up a cap dump (johnsson), an overrated middle six forward (kapanen), a soon to expire middle of the pack goaltender and a prospect with the approximate value of a 3rd all for an elite winger on a down year and a slightly worse but significantly cheaper goaltender in rittich. If they can extend Rittich for under 4M, then this is a good trade.
I actually think it is worse for Calgary than it is for TOR. TOR is getting the best player in this deal... this was just a single down year which most of the flames forwards experienced.

I can't say I would flip Gaudreau, but CGY should investigate a CAR trade for Pesce.

I never understand the thought process that the Leafs won't be able to afford Andersen. How big of a raise do we really think he's getting? How many goalies make more than 7 mil/year? Four? And how many clubs would redo those contracts if they could? The Leafs can afford to pay Andersen if they want to, the question is do they want to. I could see 6.5 maybe, but I doubt he's getting much more than that.