The moodle grade book is very powerful, good enough for me to give up using Excel for grading. Tell your teachers that by using the Moodle grade book, that they will spend much less time overall with grading. Your teachers are not beginners, they are very smart folks. However, when you put a powerful product in front of people, like Excel, then yet, it will take some time to learn.
Using the grade book as I described for activities outside of moodle is not a workaround. It is just using a normal moodle feature.