I think a Tkachuk deal likely needs more, because Nylander only has 2 years. I'd guess something like Nylander, Sandin, 1st.

As for Arizona, based on where they're at in their curve I don't think they'd place an ounce of value on Holl or Muzzin. I don't think getting a couple guys they don't value, a late 1st and a C-tier prospect gets them interested in moving Chychrun.

Btw neither Abruzzese and Steeves are not needle movers imo. They're 23 and 22 respectively, and basically C-tier prospects (maybe B-tier on a good day). They wouldn't carry much weight in return values to CGY or ARI. For perspective, if you were to trade either of them for a draft pick, I don't think you get more than a 4th for either one.

CGY would be better off trying to maximize the return to a team that will give them 4-assets similar to the Eichel trade or a young star with team control like Kyrou. Dubas definitely wouldn't be offering Nylander+3 pieces with him. Tkachuk wants to be traded to the Blues or one of the low/no tax state teams, so there could probably be a bidding war between the Blues and Vegas at the least. NYR and NJ are interested already so they will be making offers too, even though they aren't on Tkachuk's list of teams he would sign long-term with.

Even if Tkachuk was willing to go to Toronto and sign for 8 years, his the extra 2m+ on his contract will likely be the biggest difference in terms of overall impact between having him over Nylander in Toronto.