I can speak from a Tableau perspective and a general perspective about this. I have worked with a number of our customers in the past that have some sort of hybrid solution like this. Often times it is departmentally based--sales uses Tableau but marketing uses another tool, as an example. As with any comparison of software, you will find that each tool has it strengths. I would suggest that you allow your users to gravitate towards whichever feels natural to them.
From my experience, Tableau can be learned by almost anyone but it does require some effort to become proficient. If users find themselves more comfortable with something familiar, that is great too. I'd just make sure that you make it clear that people have an option. For what it's worth, everyone here at Tableau from Sales to Marketing to Development learns Tableau to some degree of proficiency. It may be that you find some people are strong analysts than you would have previously thought
It's obvious that you are and your company are putting a lot of thought into this which is refreshing to see. I hope my rambling helps a bit.