While working on T201547, I took a close look at the various UI elements and noticed that the font formatting keyboard shortcuts are shown in Visual Editor on mobile devices.
Shortcuts like Ctrl-B, Ctrl-U, etc., are not quite relevant when using the on-screen keyboard. They are, however, relevant when using a physical keyboard, often connected using Bluetooth. I tested it on Samsung Galaxy S7 with Android 8 and Samsung Galaxy Tab 10.1 with Android 5, and somewhat surprisingly the shortcuts actually work.
The shortcuts are not really getting in the way, because their appearance is grey and subdued, although perhaps removing them if they are not needed can save some screen space.
If it's possible on mobile devices to detect that a physical keyboard is being used, then maybe these shortcuts can be shown only when the physical keyboard is used.