1. Planned upgrades can make a big difference when replacing poor production. Non-Amaya catchers combined for a 45 wRC+, forty-five! Replacing them with a 85 wRC+(Jansen's career: 100, Kelly: 85, Higashioka: 81) is roughly equivalent to upgrading from 2024 Michael Busch to 2024 Freddie Freeman(to say nothing of Amaya improving on his own line). Similarly, 2024 Morel to Paredes' career/2024 wRC+ is roughly equivalent to upgrading from 2024 Ian Happ to 2024 Bryce Harper. To that end, the Cubs had largely closed any holes by midseason, they were 9th in wRC+ after the All-Star break. They've lost essentially nothing from that lineup and had little in the way of extreme over-performance.
2. The 'missing offense' is largely a function of Wrigley being an extreme pitcher's park last year. The Cubs were 24th in wRC+ at home and 6th on the road. As far as consistency goes, last year the Cubs did not go 3 straight road games without reaching 4+ runs. At home that happened EIGHT times. Thankfully there's little reason for this to continue, the renovations appear to have made Wrigley more pitcher friendly, but in the sense it went from a slight hitter's park to a neutral park, not one we'd expect to be at the bottom of park factors with regularity. This is a big part of why pitching is the focus, because the pitching staff will be harmed by that reversion to norms like the offense will be helped.