It's fine that you find the Yoshida signing to be "pretty interesting," but it might be worth being open to other perspectives. I just posted on the Yoshida thread that ZiPS overestimated Seiya Suzuki's numbers last year and would be genuinely curious to understand why it isn't doing the same with Yoshida. If you normalize the ZiPS Yoshida projection for last season's overestimation of Suzuki, you get a 50th percentile OPS similar to Kike's 2021 numbers. But Kike is an good-to-excellent center fielder. Some reports (Keith Law's, for example) suggest that Yoshida is a defensive liability who needs to be hidden in Fenway's LF or slotted in at DH. So, you're getting a 2 WAR player (inclusive of defense) for a 5 year commitment at an $18 million AAV. But Kike just re-signed for a 1 year commitment at a $10 million AAV.
And there seems to be much more downside risk to Yoshida than Kike. Kike is a known commodity who has an extended track record of facing MLB pitching. Yoshida does not. How can we be sure that his diminutive stature and lack of exposure to MLB caliber pitching doesn't depress his offensive profile? And shouldn't that downside risk have been reflected in both the AAV and duration of his contract?
Lastly, my post didn't definitively say that Yoshida's contract was a massive overpay (although I'm worried it might be). It said that I wasn't sure whether to consider Senga's contract as a positive for the Red Sox (in the ability to acquire a starter less expensively) or a negative (in that it could be inferred as evidence of a massive overpay). And, frankly, other posters have had that same reaction to the Senga deal on this thread and the MLB Offseason Senga thread (I'd recommend reading
@radsoxfan 's posts). So, perhaps it's worth weighing the evidence and reconsidering the possibility that the Red Sox F.O. isn't infallible.