I agree with your general principle. What makes cap dumps and retention interesting is teams place different values on cash paid and cap space used, and those values can change year to year for any given team.
For example Toronto would have no problem paying $6m cash for a 1st round draft pick, but $6m of cap space is far more valuable to Toronto right now then burning cap space for a draft pick.
Whereas Ottawa would be fine burning $6m of cap space for a draft pick, but $6m of cash is more valuable to Ottawa then $6m of cap space. So I’d guess they’d want more then a 1st for $6m cash.
Looking at Detroit and Arizona I think they’re both in a similar situation the next two seasons where the cap space consumed in a dump trade is less important, and the trade value would be driven more by the cash outlay side of the equation. Neither the Wings nor the Coyotes are going to be constrained by the cap.
Most of these moves are not cash flow related; most are cap space constraints. In your example we see Arizona, a team that was behind in paying player bonus money and on paying its arena rent, taking on $5M for draft picks. Why? Because if cash flow is an issue, they took on $11M in cap space for an additional $5M in payroll. That allows for a
cheaper payroll if they so choose.
The Islanders weren't trying to get rid of cash payments, they needed cap space. 2 2nds were not the price for $5M in cash over 2 years, it was for $5.5M in cap space per year which is much more valuable and hard to come by.
Trying to open up cap space was also the issue with the Leafs and Marleau, or this move with Tarasenko. If $5M in cash is too rich for Detroit (and I highly doubt that) then Carolina and St. Louis could try to find another team willing to lay out that cap space for draft picks.
The cap space is the league-wide limited commodity.