I completely understand your frustration, but for the benefit of clarity, we should be mindful that many system features are model-specific.
Split Keyboard has never been supported on 11” or 12.9” models of iPad Pro - as such, the feature has not been taken away - it has simply never been available on these models.
Given the large form-factor of the largest screen iPad’s Pro, it is possible that using these models whilst handheld wasn’t intended- or some other UI consideration inhibited its implementation.
Whilst not being able to provide a workaround for the missing feature, Apple do invite constructive comment via their feedback pages:
https://www.apple.com/feedback/ipad.html
I hope this information has been in some way helpful - if only in understanding the model-availability of the Split Keyboard feature.