I don't think it's that simple. If you send money and someone sends back something of value (prospects), is that negative? Like Did Verlander's contract have negative Value?
But if you're starting with the principle that you need to pay, then it is. You're assuming you need to eat $X per year just to get nothing back. Sure, you can eat $X+Y to get Y value in prospects back, but that doesn't mean X disappears.
The question with the Verlander trade - where the Tigers ate $8m/year for 2 years but got back 3 very good prospects - is really what those prospects would sell for. If you could have sold those 3 prospects for more than $16 million, then the Tigers were just buying additional prospects. Basically: if the Tigers had offered Verlander for a pair of used batting gloves, would the Astros have taken it? And I think the answer there is of course. Detroit ate some salary to buy additional prospects, but Verlander had some value that went into purchasing those prospects too. I'd normally have taken the fact that Verlander passed through waivers first as an indication that he did indeed have a negative valuation - nobody would take him for free if they had to pay his contract - but his situation was complicated by the existence of a full no-trade clause. Teams usually don't claim such players because the typical pattern is claim, pulled back...and then nothing, because you can't really negotiate then.
wait - His AAV stays constant - $23.333MM the length of his contract. Contract ends in 2024. You are about right in what he's owed in actual cash.
The AAV on the remaining term isn't constant, though, which is what you're asking someone to take on. The AAV over the whole length is irrelevant now because 2 years are already history.
Pretty sure many teams eat some cash in deals like that. Thought that was common knowledge
Yes, it is common knowledge. But if you're eating more cash than the value of what you're getting back from the other team, that's negative value.
Think of it this way: if the Nats put Corbin on waivers tomorrow, would any team claim him knowing that doing so would mean they'd owe him a guaranteed $106 million over the next 4 years? Almost certainly not. That means Corbin's value is, at absolute maximum, zero in trade terms.