I worked on a mobile app dev team that tried to Ui logic with the backend. With many of the justifications you mentioned being justifications for doing it that way. White labelling, A/B testing, avoiding redeploying, etc.

The result was a mess, with many of the possible concerns and drawbacks you’ve cited ending up manifesting themselves. It was an unmaintainable mess that tried to re-invent the web browser wheel badly, except using json instead of HTML. Maintaining the abstraction framework became a full-time job for people already just trying to barely deliver features on time.

And with the backend people already being busy and tied up with other stuff, the mobile app developers ended up having to become impromptu full stack developers, have to code PHP on backend to complete features in addition to the code they had to write in Objective-C/Java for their native app level portion of the feature.

The backend approach was so resented and hated by the mobile app devs that the business eventually got rid of it.