Due to how customizable SSRS reports can be it's really not possible for us to create a generic "one size fits all" recommendation for how to validate the output of the reports. Each one is unique and require a customized approach.
I agree the suggested XPATH looks very fragile. I can help in your case if you go to Step Failure Details, find and click Export and attach the generated .zip file. It contains valuable information I need, such as a snapshot of the DOM, to figure out a better method that will work reliably in your case.