To obtain your MCSA: BI Reporting you need to pass two exams: 70-778 (Analyzing and Visualizing Data with Power BI) and 70-779 (Analyzing and Visualizing Data with Excel).
I took the 70-778 last year; and was surprised, when the 70-779 exam was announced, at how much of an overlap there was between the two exams. I took the 70-779 exam in April of this year, shortly after it came out of beta; but, had they both become available simultaneously, I would definitely have prepared for and taken both exams at the same time.
And this is the approach that we are now recommending to students who attend our 5-day Power BI MCSA Certification Training course, which we run in London once a month.
The overlap between the two exams results from the common BI features found in both Power BI and Excel: namely data modelling using the DAX language; and data connection and transformation using the M language.
The approach that I would recommend is to divide the topics covered in both exams into three categories:
Study and prepare for these topics as a single endeavour, then take both exams on the same day. That way, rather than putting yourself through the preparation and exam cycle twice, you will take full advantage of the “loophole” created by the fact that both exams have so much in common.
The following chart shows an approximation of the percentage of possible topics in each of our three recommended categories.
As you can see, approximately half of the topics which you will need to prepare fall in to the common category; 40% are Power BI topics; and only about 10% are Excel topics. The reason for the disparity between the amount of preparation required for Power BI and Excel topics is a result of the fact that Power BI has so many moving parts.
You will have the same number of questions on Excel as you will on Power BI, but the Power BI questions will be drawn from a much larger pool of possible questions; and, therefore, much more preparation will be required.
If you are a seasoned user of Excel, familiar with all the options relating to pivot tables, pivot charts, slicers and timelines, you may also find that the amount of Excel preparation you require is reduced even more.
In short, why make a task any harder than it needs to be. Microsoft have made the MCSA: BI Reporting a lot easier than it might have been; so, take advantage of this fact; and prepare for the 70-778 and 70-779 together, as if they were a single exam.