The issue you have is that a team that develops those TOR pitchers do not trade them away for great hitting specs. It just doesn't happen. Which means either the Cubs overpay for older pitchers or they develop them in the limited cheap window that they have.
You don't develop pitching because it's too unpredictable between actual stuff, injury, and stamina to be a starter. Pitchers come from everywhere, if you look at the pitchers who are top 10 in WAR over the past three years, they were drafted
1-9 (Kerhsaw)
4-10 (Kluber)*
1-11 (Scherzer)
1-13 (Sale)
5-5 (Arrieta)*
2-16 (Lester)
IFA (Quintana)
IFA (Cueto)
1-10 (Bumgarner)
Now hitters
1-24 Trout
1s - 18 Donaldson *
IFA Beltre
5-18 Goldschmidt
6 - 20 Rizzo *
IFA Altuve
1-3 Machado
17 - 9 Kinsler
1-5 Posey
1-2 Bryant
* = Traded before achieved success
The Cubs built a team around defense and out creation that allows them to scout and find a pitcher who fits their needs (pitches low in the zone, generates both swing and miss as well as weak contact/ground balls) which means they can scout and sign guys that don't have electric TOR stuff but produce TOR results. Sure they paid top dollar for Lester but that's a luxury they could afford with all their young hitters being pre-arb guys. As Lester ages and the hitters get more expensive, you'll see a more balanced approach to the draft (first four years was almost exclusively hitters at the top/early, switched to pitching the past few drafts). The other parts of their rotation (Arrieta, Hendricks, Anderson, Montgomery) were low cost signings or cast-offs from other teams.
Look at the Mets, they thought they had a rotation full of TOR guys yet Harvey has been hurt multiple times, Matz can't stay healthy consistently, and de Grom has thrown less than 500 MLB innings and he's already turning 29 in June. I wish the Sox luck because they've gone that route but that's a very dangerous road to go down, especially with very little top flight hitting talent to off-set the need for pitching to be dominant in the future.