This may or may not apply to OPs app, but for mobile-first apps with a broad audience, having an identical appearance/interaction model across competing mobile

This may or may not apply to OPs app, but for mobile-first apps with a broad audience, having an identical appearance/interaction model across competing mobile platforms is a bug, not a feature. Or maybe not exactly a "bug" but at least an unfortunate tradeoff because your org lacks in-house expertise on one or more of the target platforms. The case of a single person using many apps on a single mobile platform is just so much more common than the case of a single person using your app on multiple mobile platforms that it makes far more sense to hew to the platform idioms at the cost of cross-platform consistency. An obvious exception might be something like Slack, where it's common to use both the mobile app and the web app (either directly or via an Electron-like wrapper), but calling Slack "mobile first" is also a stretch.