A2X has been built from the ground up with one basic premise, that all transactions should be able to reconcile back to the money in your bank account - as this is one data point that you can have confidence in.
We have found that when doing Amazon accounting based on order data it is very very hard to ever correctly reconcile to the payments in your bank account - fees, adjustments, reimbursements all mean that the order data seldom relates directly to the nett payment Amazon pays you.
In addition to the goal of reconciling the payments from Amazon to sales and fees, are two other motivations. Firstly, Xero recommends against having too many transactions in your accounting system - Xero should be for financial reporting, not for operational functions. Secondly, our experience is that as your Amazon business grows, the large number of invoices becomes increasingly difficult to manage and less useful for management reporting. For example if you have 100's of orders per day, you likely do not want to review each one within your accounting system but you do need complete confidence that Amazon paid you the correct amount and how that payment reconciles to your sales and fees.