"Never" is a bit of an exaggeration. I do see many cases where developers misuse B4XPages and add unnecessary code to the main module.
If you are building a non-cross platform solution then adding layout, as you wrote, sounds valid.
I would have done it differently and implement the bar in a class, and create a class instance in each of the pages. This will be cross platform, and in the long run, will also be easier to maintain.