Are you aggregating your data from order item level to daily (by delivery date?).
If not, I don’t think this approach will work since you might have multiple orders on the same delivery day. And if you then join in your -1yr data (this has to be on a daily aggregate right?) you would get the same -1yr order value on multiple order items and basically double count that.
And I agree column grouping collapsability would come in super handy 
What confuses me on this is, the enhancement to configure multiple column groupings got only introduced recently - why has the collapsability not been done along with it 
(probably more effort… but grouping ↔ collapsability are just naturally linked in my opinion)