Yes, rather than upgrading at second, they could upgrade in the outfield, with Bryant, or Marte, or Suzuki, and put Kiké back at second ....
I'm not sure this suggestion does anything to help the defense. Here are some numbers (small sample sizes and defensive metrics caveats, to be sure):
Kiké 2021 CF (716 Inn) DRS 14 UZR/150 12.1
Kiké 2021 2B (367 Inn) DRS 0. UZR/150 -1.3
The year he saw the most action at 2b, 589 innings in 2019, he had a DRS of 12, but a UZR/150 of -0.3. In fact, the only year he had a positive UZR/150 was 2014, his first in the bigs. For his career (1630 innings), his UZR/150 at 2B is -5.1. In contrast, his career (1825 innings) UZR/150 in CF is 10.1.
Arroyo 2021 2B (387 Inn) DRS 5. UZR/150 7.8
His career (only 581 innings) UZR/150 at 2B is 7.4.
Marte 2021 CF (1023 Inn) DRS -4. UZR/150 1.0
These numbers don't even represent an aging slip. For his career in CF (4480 innings), Marte has -12 DRS and a UZR/150 of -0.6.
Neither Bryant nor Suzuki is a centerfielder. Nor are Verdugo or Renfroe.
Unless the goal is to weaken the Red Sox' two most productive defensive positions, I'd leave Kiké in CF and Arroyo at 2B (unless they're bringing in someone who actually upgrades the defense). Marte brings offensive (possibly*) and baserunning (definitely**) upside, but at the cost of weakening two positions. I don't think it's worth it when defense is a bigger problem than offense.
* Marte had a 133 wRC+ in 2021, compared to Kiké's 110 and Arroyo's 106. But Marte's was an outlier, the highest of his career. His next closest was 132 in 2014. His three most recent years have been 112, 118, 108. His Steamer projection for 2022 is 110. Kiké's Steamer projection is 105, and Arroyo's is 91. Marte will be 33 years old in 2022, Kiké 30, Arroyo 27. I'd bet on Arroyo at least matching his 2021 wRC+ next year; Kiké too. I wouldn't bet on Marte matching his.
** Marte had 47 SB last year and a 12.3 BsR score from FanGraphs. Kiké had 1 SB and a 3.0 BsR; Arroyo 0 SB and a 1.5 BsR. Marte is clearly a better baserunner.
One more point. FanGraphs rated the 2021 Red Sox as being 6th in 2B WAR (4.7) and 5th in CF WAR (5.2). The other positions came in like this: C - 21st (1.3), 1B - 21st (1.6), 3B - 5th (4.7), SS - 5th (5.2), LF - 13th (2.4), RF - 19th (1.8), DH - 2nd (4.3).
By exercising the Vazquez option it seems like they don't plan to upgrade catcher, though that's an obvious place for improvement.
Ditto for 1B, but do they trust that Bobby D will continue to improve? Even so, a LHH to platoon with him would be helpful; maybe that's what Bloom means by saying Schwarber "fits us."
RF is the next position that could stand an upgrade. I loved Renfroe's arm out there, and he made some plays. But he also didn't make other plays. FanGraphs gives him 0 DRS in RF for 2021 in 1166 innings, and a -2.1 UZR/150. He put up a 114 wRC+ with -2.6 BsR, and his Steamer projection for 2022 is a 110 wRC+. Kris Bryant wouldn't be a better defender in RF, but he would bring offensive and baserunning upside. Call me crazy, but I think RF looks like the most likely position for an upgrade. Move Renfroe and either bring in a FA or find a better Renfroe among this year's non-tenders, or trade for one.