For one thing, ERod might not actually face Cole in a head-to-head playoff series, but of course, I'd take Cole. It would not be a slam dunk. ERod finds ways to win. Period.
As for other team aces, I don't see the purpose of looking at a 6 week sample size to determine who he's better than. Taking a 2020-2021 sample size is rather small, too, and ERod did not pitch in 2020. Going back to 2018 and including all seasons in-between, here's how pitchers are ranked in various categories. Let's say the top 30 are "aces."
Without looking, I'd view ERod as one of the game's best #2 starters and likely better than half the team's #1, but here are some numbers.
2018-2021 (150 pitchers with 170+ IP- that's 5 per team)
Wins (more of a team stat, but still...)
47-14 Cole
38-16 Bieber
38-15 Verlander
38-20 Greinke
37-12 ERod
37-20 Nola
37-27 Gonzalez
36-20 Scherzer
36-15 Kershaw
35-13 Morton
(Some of these guys are now hurt or extremely aged.)
ERA-
49 deGrom
57 Ryu
60 Verlander, Cole
65 Clevinger, Soroka, Gallen, Scherzer
68 Sale
69 Kershaw
70 Bauer, Bieber
71 Snell
73 Buehler
74 Kluber, Means. Plesac, Glasnow
75 Nola, Woodruff
32. ERod 83 (slots as a top #2)
xFIP-
59 Sale
63 deGrom, Cole
67 Bieber
43. ERod 90 (slots as a mid #2)
WHIP
0.85 Verlander
0.92 deGrom
0.93 Cole
0.97 Sale
86. ERod 1.30 (slots as a low #3)
WAR:
14. Sale 9.8
43. ERod 6.3 (not bad missing the 2020 season)
It's one thing to say, I'd rather have this starter than that one, but age, contract status, past history and future outlook.
If you go by just past performance and weigh the last 2-3 years more heavily, my guess is ERod can be slotted anywhere from #20 to #40 without much argument from me.
Erod is a winner, and while using wins is not something I usually do, since run support, park dimensions, luck and strength of opponents play into wins, ERod is unmatched since 2018.
19-4 in 2018 (17 games with 0-4 run support)
26-8 in 2019 (8 games with 0-4 run support)
5-2 in 2021 (2 games with 0-4 run support)
50-14 last 4 years (27 games with 0-4 runs support)
14 Slam dunk better than ERod:
deGrom
Cole
Scherzer
Bieber
Bauer
Nola
Morton
Sale
Kershaw
Buehler
Snell
Gray
Strasburg
Woodruff
I can probably name 14 more that are better. I'd put him around #30-35.