Speaking of SP'er depth, I agree it is very important, and for once we seem to have top quality SP'ers and depth. Quality AND Quantity!
It's interesting to note that our ring seasons were often led by just 5-6 key SP'ers, where very little injuries occurred and the need for depth, especially extended depth was simply not present.
2004: Amazingly, we only needed 5 GS outside our starting 5: 33 Pedro & Lowe, 32 Schilling, 30 Wake & 29 Arroyo.
2007: There were only 11 GS outside the top 6 SP'ers. 32 Dice-K, 31 Wake, 30 Beckett, 24 Schilling, 23 Tavarez, 11 Lester.
2013: A little more depth was needed, and even a trade for Peavy: 33 Lester, 29 Lackey, 29 Dempster, 27 Doubront, 16 Buchholz, 10 Peavy and 17 GS by 5 others. Those 17 GS were all pitchers who added zero value as starters.
2018: Kinda breaks the mold, as the depth helped, and the trade for Nate might have won us that 4th ring: 33 Porcello, 30 Price, 27 Sale, 23 ERod, 13 Johnson (4.17) 11 (3.33) 11 Pomeranz (sucked) 8 Velazquez (3.18) 4 Wright (2.68). Still we probably win without Johnson & Pomeranz and just needed the Nate trade to give us 5 SP'ers.
Other seasons that seemed like near misses:
2003: 4 starters over 29 GS w Fossum & Suppan going for 24.
1986: 4 starters over 25 GS and 16 from Seaver, 13 Sellers and 10 Brown.
1978: 102 GS from 3 guys, 24 from Lee and 27 from Jim Wright + Ripley
1975: 114 GS from 3 guys, 20 from Cleveland, 16 Moret & 11 from Pole.