These long contracts never end up well. See Angels Pujols, Tigers Miggy, etc. usually last half of contact production falls way off.
In the post-steroid era players really fall off after age 34-35 like they did in pre-steroid era. There are exceptions of course but not many.
Current contracts like Stanton, Rendon, Strausburg, Bum Gardner, Sale also come to mind.
Especially for a player who now definitely has a history of arm trouble. If by chance he can’t pitch or gets hurt again you’re paying 70 million a year until he’s 40 for a hitter? An awesome hitter now but how will he be 6, 7, 8, 9 years from now?