This contract weas likely designed for shock value. Him (and his agents) likely had the goal of beating the 674M record and they did it.
When we get the details, it'll probably make a little more sense. Mackus has done some of the math, but if he does something crazy like defer 500M, then the NPV of the contract takes a big hit. We'll see, but if the "value" of the contract is 500M (like big money deferred out over 20 or 30 years)....nobody would have batted an eye at 10/525.
So they agree on that number FIRST then Ohtani and his agents go play the math game and come back with the deferred structure cost to get the perception that want. It's been done in the past (Mackus correctly points out the Chris Davis contract which was exactly this) and you have some other similar examples like Max Scherzer....but they've intentionally done this on a completely different scale.
In other words, they didn't agree to 10/700 and then Ohtani (per the public narrative) says he wants to defer it out for LAD flexibility....they agreed to a much lesser number then Ohtani/agents came back with the deferred structure to get them where they wanted to be in the National discourse.
Each level of this is being managed to elevate Ohtani's International profile.