It definitely is a set up to shock the audience, Ichibe did seem like a monster in that battle. But that's not what I'm saying.
A lot of fans were complaining because the seemingly Invincible Sternritters from the first Invasion were being bullied at every battle, their elite Royal Guard was owned and Yhwach on the ropes. Fans in the moment were rightfully annoyed because the treatment of the antagonists was so poor.
So while the Ichibe v. Yhwach battle actually ends up being pretty cool, reading it weekly after watching the Soul Society collectively stomp on the quincy's are aggravating.
The Sternritters being initially dominant and then getting overwhelmed isn’t really relevant since Yhwach ultimately discards them as disposable pieces. They were tools to destabilize Soul Society and buy him time to awaken The Almighty and fully absorb the Soul King.
So when Ichibe nearly deletes Yhwach from existence it’s not poor writing, you can only truly appreciate Yhwach’s overwhelming threat when he comes back from something so definitive as being erased from name and the Three Worlds themselves. That’s what made Yhwach terrifying as a villain, not his brute strength, but the cheat code that is the Almighty.
The "annoyance" fans felt was exactly what Kubo wanted. He built up the hype: the Sternritter storm in, bodies drop, Byakuya especially turned into blood pulp, then the Royal Guard show up with their training sessions and we think, “Okay, now the tide’s turning.” Ichibe comes in like a primordial god that defines the very title of the Manga "
Bleach",, wipes Yhwach’s name, his power, his very existence… and then boom, The Almighty hits, and suddenly
none of it mattered. That’s the point. Kubo made us believe the Quincy could lose. He gave us that hope and then ripped it away. The Almighty doesn’t just win fights; it rewrites reality like the fight never even happened. That’s not bad writing, that’s peak writing.
I don't generally like Kubo's writing, but he absolutely nailed Yhwach's rise to power.