2020 doesn't really count.
I think the common point of reference here should be Cora. And not Cora as an isolated decision-maker, but a key figure in implementing overall strategy and philosophy.
2018 - featured career players in their prime guided by a "stay the course" player's manager.
2019 - more or less the same club, but a slow start equaled missed playoffs, and probably some correlation to the "stay the course" style. I don't know if you all recall, but we were constantly promised: "it'll get better."
2020 - Cora suspended, whacky season overall. I'm not too stuck on using this as predictive in any sense.
2021 - fast start for a team many wrote off. Faded in late July and August until outside help was added. (Covid forced roster change, so "staying the course" was not an option.)
At the all-star break (July 11) the team was 55-36 and Boston was 1.5 games up on Tampa in the AL East. I'm cherry-picking here, but by Aug 10, they'd fallen to 65-50, five games behind the Rays.
July - Rios and Robles picked up - solid pen additions.
Marwin Gonzalez released Aug 12. .414 OPS in August.
Schwarber, began play Aug 14. .959 OPS for the rest of the season over 168 PAs.
(Also tinkers with Dalbec per reporting sometime after he was acquired on July 29. Dalbec has 1.205 OPS in 72 PAs in August. Then .928 OPS in 85 PAs in Sept.
Shaw, acquired Aug 15. .843 OPS over 48 PAs.
Iglesias acqired Sept 6. .915 OPS over 64 PAs.
2022 - shades of 2019. Slow start, stay the course mentality. "We know deep in our hearts that we're a better team than this, so by golly, we're just going to keep with the same shitty approach."
In retrospect, in 2021, Schwarber was a great pickup, both for his own impact and his influence on Dalbec. Shaw provided adequate spelling and a bat off the bench, while Iglesias locked down the IF defense and was a huge upgrade over Arroyo. But I wonder if the final two moves were not made due to the Covid shakeup. In an alternate world, Marwin would have stayed with the team, and they may not have squeaked into the post-season by the skin of their teeth.