A 12-13 year deal would take Ohtani to age 40-41, so there would definitely be some dead money in there unless he defies aging on top of all the other great things he can do, but he's not Pujols or Cabrera. Aside from his ability to pitch, he's also a great athlete, plus base runner, and if he needs to take a break from pitching then he can likely transition into a plus defensive OF for a few years, so he'll be able to provide value aside from his bat (which is elite). That's not even factoring the marketing aspect and how much he changes the Jays "brand".
So yeah, if the Jays actually pull off this miracle and sign him, you can certainly dread what his production could look like in 2030-35, but I don't think too many Jays fans would care about that in 2023.