Maybe. Let's take the extreme case and see he produces nothing the rest of the deal -- would you take a WS now in exchange for 29 mil of AAV for 10 years? Maybe that's not a bad trade -- I genuinely don't know where I'd draw the line.
I edited my post because WS win is a boring answer and I don't necessarily buy it. Maybe if it was 2004. I think there's a chance he ends up being worth his contract anyway but I doubt the Dodgers get much surplus value. Plus it's possible they would have won the WS even if they didn't give him the extension. He still would have been on the team. So... I'm sticking to that. Dodgers didn't need to give Mookie the extension, he was under their control.
I think the correct thing to do is to target the Trevor Story's or maybe even Xander's who might take 5-6 year deals thru their age 30-35 seasons. You don't get any of the dead end years and you have a better idea of how he'll hold up in his ages 30-35 seasons. A player who was good at 29 is more likely to be good at 30 than a player who is good at 25.
And while $9m/war in FA might be the average, I don't think it's a good use of resources if you end up at exactly $9 mil/WAR when it's attached to mega deals. If the Sox signed Devers to a 10y/315m year deal and he put up 10 identical seasons to 2021, would people be happy with that? I mean, maybe some would. Is that the player you want to lock up all those resources to? It's not an awful result, but it's pretty meh. If you are offering him 10y/315m, you want 2022 production. At least for the first half of the contract.
Lester is probably a bad example and more a semantic argument than anything. But if Jon Lester is considered a good outcome, it shows you how bad the value in FA actually is. He had 1 great year (5.6WAR), 2 decent ones (2.8, 2.7), 2 Workhorse years (0.8 WAR, 0.6 WAR, 352.1 ip) and one bad year that was shortened to Covid (-0.2 WAR) and then was bought out for $10 million. That's what $155 million gets you. Or by ERA+ (114,171,101,125,96,86). His era+ for the Cubs was 115.
I hope the Sox build with 2024 in mind. Use 2023 to break in the wave of pitchers (and a few positional players) coming up, sign a few stop gaps for a year. Then use 2024 to break in the wave of positional players. For the positions that are empty, sign a couple Trevor Story's to 5-6 year deals to fill out the team since they'll have cost controlled players. Sign a few pitchers to 1-2 year deals if need be. Then when those cost controlled players are up for FA, so are the older Trevor Story types, freeing up money to sign the home grown talent who will take Trevor Story deals, continuing the cycle forever. Avoid spending big money on any FA pitching because almost all of them come with injury history and because Jon Lester is considered one of the better outcomes. Rely heavily on the farm for pitching, whether that means developing arms or trading prospects for for arms.
Long story short, mega deals should come with mega production. If it's coming with $9m/war, meh.
If you knew for an absolute fact a player would provide 4 WAR every year for the next 10 years, would you offer him 10years/360 million? Does position matter? Ok, let him play any position you want.
Honestly, I think I'd rather sign a player for 10/360 who would be guaranteed to provide 8 WAR his first 5 years and 0 WAR the last 5. I wouldn't want to do either. Only 10+ year deals I like are the ones that buy out like 4-5 years of arbitration. I'd might be looking to do that with Casas and Mayer. That's risky too though. Had the Dodgers locked up Cody Bellinger after 2018 it would be panned right now as an unnecessary commitment.
Baseball really is broken. If players were FA after 4 years of service time instead of 6, how much does the $$/WAR go down? Probably a question for another thread.