Certainly, one post season should not be used as a template for others, or this year, but let's look at 2018 and the pitching usage:
GS: 5 Price, 3 Porcello & Sale, 2 Nate, 1 EROd. This confirms that only 3, maybe 4 starters are needed.
Now, IP
26 Price, 22 Nate and 15 by Sale and Porcello totalled 69 IP and 54 by the rest. If you add the two top RP'er IP it's 91 out of 143 IP or 64% of all innings by 6 guys.
The 6 for this year might be...
Crochet, Bello, Gio & Tolle plus Whitlock & Chapman,
Not too bad.