Double retention for ability to acquire another piece later.

Give the ability to have three centers able to be top 6 quality.
Canucks top 6 becomes Boeser, Petey, Miller, Mikheyev, Lindholm, ??? (many options for that)

I have a better idea. Calgary makes a lowball offer for your 1st line center to be our 2nd line center. Lindholm is a 1st line center Calgary won't be selling low on him and to a divisional rival yet.

AZ isnt retaining 50% (leaving only 1 slot) for a 4th - they have 14 picks already

Do the Canucks (or maybe Canucks fans) just not trust J.T. Miller to be as good as he has been going into the next seasons ahead? He's on pace for 100 points or at least close, that's a pretty good 2nd line center if you ask me. All the J.T. hate tossed around during the offseason appears to have been unjustified (I was doing it too, at least questioning the guy).

The Canucks should upgrade the wing first before center. If Kuzmenko isn't working out, then after Boeser the next best guy is Mikheyev? I think they want another scoring winger, which is why Guentzel has been linked to them in rumors.

It's so they can run lotto line

Exactly this. Run the Lotto line, while having a second line that actually can function without EP40 on it.
Since I argue the Miller, Boeser line is our top line this year. With EP40 carrying the second line on his back. While our Thirst line has really stepped up to be a pseudo top 6 line.