The reason New Receipt and New Payment are not meant to be standalone buttons on invoice views is that if they are, they imply that these buttons need to be used as part of a certain workflow. But there are also workflows that do not require ever clicking these buttons.
For example, if your customers always pay by bank transfer, you would typically never create receipts manually. You would import your bank transactions and then have receipt rules to allocate already-created receipts to the correct customer. You never create a new receipt from scratch.
Moving the New Receipt button under the Copy to button makes the function appear more like a utility rather than something special. For those who are creating new receipts manually, it is still the first option under the Copy to button (which takes one extra click). For those who don’t create new receipts manually, the button is not there to imply they should. It’s a compromise.
If your argument is that “One extra visible button surely cannot hurt anyone”, this is not just about one button. It’s about the general principle of keeping Manager simple. If I would cave in to everyone who says “just put there a button/checkbox/option - it’s just one - who doesn’t need it can ignore it”, Manager would look completely different. I’ve seen accounting software where creating a simple account in the chart of accounts came with 50 different form fields. No doubt there is a passionate user behind every form field but when you zoom out, it’s a complete mess nobody wants to use.
If your argument is that this button is used by many users so exception can be made. Fair enough. But still. Where do I draw the line? How many users is enough to justify the exception. I don’t know. So I err on the side of consistency. Every View screen in Manager has identical buttons.