It could easily have been $600 million, probably $700 million. To get into a real debate, you might have had to double this extension to $860 million. Mike Trout might be worth a billion dollars over the next 12 years.
The math to get to $430 million is so simple it's almost laughable, so let's just blast through it: A "win" added on the free-agent market typically goes for around $10 million. That price has gone steadily up for decades, so with inflation one could easily estimate $15 million per win by the end of this deal.