I think any of the scenarios you presented could be great or terrible for customers depending on how they are implemented and to what end.
For example, with scenario 1, is that central R&D budget more, the same, or less than the combined budgets of the brands individually? Will that centralized R&D treat each of the participating brands equally or will some get de-prioritized in favor of others? Is that R&D focused on innovation and bring new value to customers or designing a new 3d printer to remove as many watchmakers as possible from the payroll? The value to the end customer varies dramatically based on how such a structure is implemented, funded, and what the goals are so I think comparing these is tough. If the end goal is bringing more value to the customer I'm for any of them.
What we see from Richemont seems to be a consistent effort to consolidate with the intent of cost cutting at the expense of the customer. Cutting costs and maintaining or even increasing product and service quality is admirable, cutting costs at the customer's expense without telling them is dirty. I see no innovation or additional value coming from how Richemont is using Fleurier across brands in the same way I don't see the service quality or customer experience being enhanced through the shared multi-brand Richemont service centers. Quite the opposite. Maybe pulls up Baume and Mercier....