At one point they were scummy enough to automatically add their referral codes to any Amazon link you see.

To be clear, that means Brave is ① invading their users' privacy, and ② stealing money from web publishers.

The point of referral codes is to reward web publishers for referring users to a product; leading to the user buying a product that they otherwise wouldn't.

Your browser isn't introducing you to a product. For it to insert referral codes for the browser vendor's benefit is stealing money.