You have to be realistic on some level - we're asking Betts to never put himself on the open market ever - which is wildly unrealistic. It would run counter to anybody's wish in any part of their career. If he's going to give up his free agency, then he has to be paid up front for it. Now how much of a raise should be get on his arb figures - because any such contract would require one. So let's say 3/75 for the arb years ... and then 3/100 for the free agency years - and that gets you to $185M (I did not do the math seriously in the 200). It's a deal which can manage risk for both parties. I don't worry about Betts' last 4 years as much either - but I don't see why he'd ever want to give them up, especially given he'll probably be able to get a ton from somebody by then.
As I have noted - I have zero interest in the luxury tax hit. There are ways to control for that - and if that is going to drive Judge Smails, er, ownership's thinking ... after monetizing every square inch of the Nation - he is in the wrong business. It's a budgetary choice (he is eating well either way).