Maybe they weren't aware of the bug, steering is a good method to quickly improve the model, more popularly used to refuse unsafe queries. Qwen researchers do work on interpretability and try to make it practical in production: https://arxiv.org/abs/2605.11887 , I've read this paper this summer. Overall yes, when you edit weights what often happens is that performance deteriorates elsewhere, this generally scales with how destructive your method of editing is and how expansive your edits are. Analogous to if you use a jackhammer and touch every surface in the house versus using a small chisel on a door frame.

My hope that in the future new methods will be better at editing larger scales without significant deterioration, maybe even performance increase instead.