This article is a week old now (https://blogs.fangraphs.com/the-cubs-are-finally-putting-their-run-differential-to-good-use/), but long story short, besides the last two nights, we weren't getting much benefit from those situations:
The Cubs have blown 21 leads, but they also boast 22 comeback wins, per Baseball Reference. Meanwhile, their 10-12 record in one-run games is bad but not atrocious. On top of that, they haven’t faced any more position players pitching than the average team, and in fact, they rank dead last in run value produced against position players, per Baseball Savant. They also rank ninth-last in run value with a position player of their own on the mound. Clearly, they aren’t padding their stats in non-competitive at-bats.
The Cubs have been on the winning end of blowouts more often than not, and they’ve shut out their opponents more often than they’ve been shut out. That said, even if you remove the blowouts (5+ runs), they still have a +13 run differential, or a .520 Pythagorean expected winning percentage per Baseball Reference’s calculation. If you remove the shutouts, they still have a +25 run differential and a .526 winning percentage. All this to say, the Cubs haven’t just run up their run differential with a few lopsided victories. And even if they had, it’s not entirely fair to look at the numbers without blowouts and shutouts – that’s how good teams win.