For reference here let's compare who they played last year. Vs the Giants they went Cueto, Shark, Bumgarner(who didn't pitch well but the cubs blew the game), and Strickland into Matt Moore after 5 pitches. In the NLCS they got Maeda, Kershaw, Hill, Urias, Maeda, Kershaw. Cueto is good but he's more comparable to Gio IMO. Shark is a #3. Bumgarner on top of his game is Stras/Kershaw level but clearly he wasn't. Maeda is worse than Gio IMO. Kershaw and hill are the same obviously. Long story short I don't think that run is any where near comparable to the way Stras pitched in game 1/4 and Scherzer/Gio in games 3/2. Gio obviously didn't have it game 5 and neither did Scherzer which is why the runs came.
Either way, my point here is the cubs did score on these pitchers. Game 1 vs Stras they obviously won 3-0 scoring twice on Stras and once on Madson. They scored three times on Gio in game 2 and were up 3-1 headed into the 8th where the BP blew a save giving up 5. Vs Scherzer they dinged him for 1 run and he left in a tie game which the cubs eventually won. Game 4 Stras just shut everyone down. Game 5 they obviously put up 7 on Gio/Scherzer. In game 1 vs Kershaw the cubs were up 2-0 early. Dodgers came back and tied it 2-2 when Kershaw left. Last night Russell gave them a 1-0 lead. Dodgers tied in the 5th and the bullpen blew it in the 9th.
So only in 1 of those game were the cubs behind when the opposing starter left vs 6 fantastic outings by starters. If you want to argue the cubs need to do more against the opposing bullpen that's fine to debate. But clearly their own bullpen has lost them more than their offense has. The idea in the playoffs is to hold serve as best as you can til you can score. The cubs bullpen is often given up numerous crooked innings which seals the game away.