Any metric or KPI is going to get gamed in harmful ways if it’s prioritized too highly. So the answer is to use A/B testing to make sure you’re not regressing on the goals of a design change, and judiciously, to validate whether your change is moving things in the right direction.
But beyond that you have to do the hard slog of mastering the discipline of UX, real, human-centric design, and accept that not everything important is measurable.
We have plenty of examples of how doing real UX instead of playing a numbers game can differentiate your business, Apple has applied this philosophy consistently over many years.
The root of the problem is a “fuck you, market share at all costs” culture that has come to permeate Silicon Valley. And you can argue (somewhat cynically) that this philosophy makes sense in a blue ocean where you have no competition and just need to gobble up people and turn them into cash before someone else does. But I think going forward this mentality may actually become a liability as more humane alternatives to heavily despised products emerge. Many of the current crop of giants seem to have forgotten that a company’s most valuable asset is always its brand.