Certainly, some player's contracts are more "underwater" than others, but I think the term is useful.
We'll probably never agree on how much underwater Eovaldi's contract is. The BTV has him at -10.2, so they basically are saying he's worth $11.9M x 2- not $17M x 2. ($17M salary- $11.9M value= -$5.1M per year). I'm not saying they are the foremost authority on projected value, and I actually think he's worth more than that, speculatively thinking, but I doubt any GM would give him more than $11-12M x 2, this winter. Injury prone pitchers have gotten more than that, selectively here and there, so I don't know if there is one GM out there who would offer more.
I'm fine with keeping him and hoping he can give us one full season or even moving him to the closer role to try and improve the chances he can stay healthy, but when you look at ways we can free up some salary space to add more or better players, his name is near the top of any list for doing so.
What is the "break even point" for JD? Half his salary? 2/3? 3/4? There's usually not a big rush to sign DH's, but maybe he could attract someone who thinks he can play corner OF, perhaps with a short home field OF.
Sale won't be traded. Trading Bogey might make sense due to the opt out, but if we are looking at winning in 2-3 years, it's hard to see that without Bogey.