how did bautista and ee do at ages 32 33 34 35 36?
JB: 4.3, 6.5, 4.5, 1.5, -0.5 WAR (16 WAR total in 5 years)
EE: 4.5, 3.9, 2.5, X, X (10.9 in 3 years)
So yeah, if you think you're signing JD in his one and only chance at free agency for about 150/5, he'd probably roughly be worth his contract. But you're not getting JD for that price - to sign him right now, you're going to have to give him 35 a year, around 5/175, or add in a 6th year. Sure, those might be fine for the first 2-3 years of the deal, and at the very least by the time the contract is underwater, you're likely out of the Tulo and Martin deals.
It's not the worst thing in the world, depending on what exactly you lock him down for, but it really depends on what you're looking for. If you think the window is the next 2-3 years, then it's a good deal for that. If you think it makes more sense to punt the next couple years and regroup for when Vlad+Bo are ready to contribute, then it would be a horrible deal.