i would argue that the philosophy of android is you can personalise it to your liking and this applies even to stock android phones like some people prefer swiftkey some prefer the google keyboard
using a phone out of the box, no launcher no customising etc that sounds more like the apple ecosystem mindset where you really do use what is provided, like it or not (cos you aren't offered variety of choice unlike android)
Not sure if the idea of customizations should even be relevant, and to what extent those customizations should be. Imo that is something widely used to compare android to ios many years back. Like when i was using my s2.
These days people want fluid experience out of the box. Some minor adjustments like choice of keyboard app, mail app etc is fine.
Because these days people care more about performance. In the past people just wanted to customize their phones to their own liking without the concern for performance. Download this skin, that theme. All of those are additions that run alongside the native system.
And if some of the apps are rogue, meaning to say not properly developed, they can cause issues with interaction and thus user will experience performance issues.
I used to use swiftkey on my s2, redmi note, zenfone2. But stopped once i used the new gboard on my p2xl.
It has integrations with google translate, one of the key reasons i like the now gboard. If you dont need this feature i can understand why not gboard then.