Mookie had 1 year worthy of 420 million IMO. That was 2018, a truly great offensive year. Not that he wasn't a very good offensive player in other years, just not to the level I would commit to that money. Defensively he is great, but we know that can and will decline over a 10 -12 year period
How he does in LA will play huge in what he gets offered as a FA I think. A great season dispels doubts about how much Fenway and 100 PA a year against Orioles pitching played into his numbers, not to mention whatever went on in 2018 in terms of stolen signs. I doubt he breaks 400 million but 350 seems reasonable . A rough year and he might be happy to take 8/200, and might very well land back in Boston.
Its kind of sad that young fans cant expect to see a player of Betts stature play his entire career for their team, but thats how it works today. The good thing is one can follow your favorite player no matter where he ends up. Its not like 40-50 years ago where your fav player ending up on the WC for a NL team was like being sent to Siberia, never to be seem again except maybe a couple of games a year on a national broadcast.