I have no FAANG experience but I’ll comment if that’s alright.

A few potential talking points:

BFF pattern allows you to separate concerns, have different team topologies and development methodologies, and technical standards and values for different parts of the system. Leadership may appreciate your arguments if you can put them context of enabling teams to advance independently and have different priorities which could otherwise be in conflict. An example could be efficiency gains from fronted / client oriented teams not having to switch language to work on BFF if using node. Another could be testing standards / code coverage for platform APIs may be higher than necessary for more experimental client related work.