I think the word 'overpay' gets tossed around way too much. It's a classic armchair GM word. They don't usually pay the guy that much out of the goodness of their heart. They do it because that's what it takes to get the player to sign.
Did Yamamoto get overpaid? Most people would have to agree that his contract is pure insanity. $325 million plus a $50+ million posting fee, for a guy who has never played in MLB.
But most Sox fans probably wish it was us.
And of course, if Yamamoto underperforms, we'll all be mocking the Dodgers.