I don't know if it's a useful exercise or a fair way to think about the flat cap and acquisition cost this way but say you are Tom Fitzgerald and you have 2 proposals on tap a month ago.
Ty Smith+3rd for Marino (5YRSX4.4M) and 3rd+4th for Bjornstrand (4YRSX5.4M). Or you have something that the Canucks are asking for 2023 1st, roster player, top prospect which for the sake of argument I will go with 2023 NJD 1st, Haula, and Holtz (Haula is meh but Holtz is a good pick up so I am sticking with that to balance out the value,). Miller comes with a Mika Zibanejad or F.Forsberg type extention is place. He is 2 years older so 6YRSX$8.5M which I think is a very fair end of day contract, it could even be 7 years if the newly acquired player has all the leverage in extension talks.
If you're Fitzgerald, do you go with Bjornstrand (27-30), Marino (25-29) signed throughout their prime at combined $9.8M while giving up Ty Smith, 3rd, 3rd, 4th and retaining 2023 1st, Haula, Holtz or do you go with Miller (30 at $5.5M, 31-36 at $8.5M) while giving up 2023 1st, Haula, Holtz and retaining Ty Smith, 3rd, 3rd, 4th. The extra defenseman you'll need to fill Marino's spot in the Miller route is going to cost another at least $1M in cap so the cap usage washes.
Year 1 with Miller at his prime, age 30 at $5.5M, I would take Miller that year. Year 2 Miller's raise kicks in and the cap between Scenario 1 and 2 is a wash. If Miller is a 90+ point player I would give the win to Miller route assuming Holtz isn't bashing heads in the NHL yet. If in year 3 Miller (age 32) is a 70-80 point player, the overall value of having 2 ELCs ready to help (2023 1st rounder, Holtz) and still in their prime Bjron (29) and Marino (27) may very easily outweight Miller as a 70-80 point player at $8.5M.
There are only going to be more and more of these Marino and Bjornstrand trade opportunities for GMs that have cap space and keep it open until another GM is backed into a corner.
For players in their prime like Fiala and Tkachuk, the acquisition cost can be justified. Miller's value has always had to be a deadline no cap no worries no extension type of a return. unsurprising he didn't go last season or so far. Miller is worth too much to the Canucks' chances next season to simply do what Kyle Davidson is doing when he knows he's tanking and should get the rebuild started ASAP even if the value isn't great.