There is no other way to average across rows than what it sounds like you are already doing.
In general, the program works best with less columns and more rows. That is referred to as a long format rather than a wide format. To get convert to a wide format, columns can be ‘Flatten’ to a long format.
The long format gives you the most flexibility in terms of being able to calculate a mean by grouping using x or y, both, or some other category using the Pivot command.
Here is an article describing this approach:
How to Flatten Data
Data can then be extracted from a the Pivot command to view columns of data. Or use the commands you have and add a mask. If your are used to the wide format, this may take some adjustment but it will give you a lot more flexibility.
If you are not sure how to use the Pivot, we can help with that.