I know how you want QuickBooks to work the way you want it to be. But I'm here to help you with your discount, Anattic. 

You can follow the steps provided by @MaryLandT on how you can add a discount per item in an invoice. This may be a basic thing but the workaround provided is one of the closest alternatives that you can use.

Also, while this has already been submitted as feedback, I know that QuickBooks is working for a permanent fix on this to provide a resolution.

For future reference, you can also run reports in QuickBooks Online to track the information that you need.

Reply to a comment below if there's any help that you need. Remember, I'll always be right here if you need further assistance.