You mention IT and Strategy vs. the Business.
The Business is using PowerBI to address from what I see as IT not being able to create insights fast enough to suit them. And you note how the more complex the isolated solution is, the more likely it will fail over time.
Is there any support from the IT side to define a true Data Warehouse that will tie things together better? And then place ideally 1 cube on top of it to expose to the users?
The 1 cube would mean that the data would be much more normalized and all many measures to easily be placed next to each other. A big plus is that if multiple users are using the same cube, they will all get the same results. 

Part of what you describe is far too common - the idea that if you give all the users self service tools, it solves everything.
Reality in most enterprises is more of a mix - the bulk of data used resides in a more structured source, with business rules enforced in creation of dimensions and measures.
KPI's can be built to serve the bulk of the needs, with ad hoc filling some gaps, and some Power Users able to help give IT direction for future expansion.
What direction the company heads - a key is Business and IT being able to get together and being able to come up with a list of what is working well (and not so well) for each, and come up with a 1 or 2 year plan to present to upper management. 

Both IT and Business need to be able to work together toward similar goals. Clashing and not creating solutions never works. The divide can easily become greater as IT is more measurable for time. You may stage some data for consumption, and it may have taken you a week to get it into production. From the Business side, they only count the 5 minutes to create the report. And since most in the business creating reports have other job titles, they do not separate out any development time. It could be 4 hours, but if they say it was 5 minutes, it is 5 minutes.