Yes, it will most likely come down to the rotation.
The first issue is, of course, health. I feel pretty confident in 4-5 of our SP'ers, when healthy. Guys like Mata and Walter may surprise, if they can stay healthy, too.
The skill levels of our SP'ers, assuming no major age or injury-related regressions is pretty well proven. However, one should expect age regression (Kluber & Sale) and/or some time needed to return to form after dealing with injuries or surgery(Sale, Whitlock, Houck).
Sale turns 34 in a few days and hasn't put together a full season of greatness since 2018. He did have an ERA+ of 118 from 2019-2022, but only logged 196 IP over those 4 years. It's hard to know, if he can even post a 118 ERA+ over 170+ IP, this year.
Kluber turns 37 in 3 weeks and has 2 Cy Youngs under his belt, along with 3 other top 9 finishes. His last great year was also 2018. He has posted a 91 ERA+ since then, but did log 164 IP, last year. He posted a 112 ERA+ in 2021 in 80 IP with the Yanks, but it's hard to expect that over 160+ IP in 2023. I'm hopeful, but maybe just being a homer on Corey.
Whitlock turns 27 in June, which is often peak prime for many pitchers. He is coming off an injury and has not gone over 120 IP since 2018 (in the minors.) He's got some nasty stuff, and the big question seems to be how many innings can he give us, not his talent level.
Houck also turns 27 in June. He's posted some eye-opening numbers over his first 3 seasons in the bigs, but like Whitlock, it's about IP. He has a 150 career ERA+. His biggest struggle seems to point him towards long relief- not the rotation:
.504 OPSA first time facing an opp
.647 OPSA second time
1.017 third time, but the sample size is only 30 PAs.
Pivetta just turned 30, so is still in prime. He's been pretty steady for us at a 99 ERA+ and 31+ starts a year. He may be one of the league's best 5th starter, if we can fill the top 4 slots with guys better than him. He's had some long stretches of solid pitching within each season, with us. My hope is he can put together s 32 start stretch like those shorter ones.
Bello turns 24 in May and showed some promise after a rough first start or two, last year. He may be one of our biggest wild cards, but I'm very optimistic about his abilities.
Paxton is 34 and may be healthy by April. He had over 150 IP in both 2018 and 2019 with a 112 ERA+ over those 2 seasons. 23 IP over the last 3 seasons is the killer, but this guy may still have one good season left in him. 34 is not all that old.
7 SP'ers and only 5 needed. We may get by with 4 pitching well or even 3 pitching very well, as long as the others don't suck. having mata, Crawford, Winckowski and Walter as ML ready depth may also help.
I feel pretty confident we can find the right 5 to lift us to 2nd or 3rd place, but certainly 4th place is a reasonable expectation.