I agree, it’s very tacky to have an permanent ad on the main screen for users already paying at a lower (yet still not cheap) tier. I contacted support about this and was directed here. Here is the response I got that commented on the button:
Since we launched our new Business Tier, we have placed a few upgrade prompts throughout the product (similar to how we have Premium upgrade prompts in our Free version). Unfortunately we are not able to remove this prompt, but I can certainly take this to our Product’s team for consideration as feedback.