I have this page. This page is a combination between a "congratulations" and "here's something else to do" sort of page.

The very first piece of content (besides the header/nav) is a large block with a high contrast background that says looks like this:
[![enter image description here](https://i.stack.imgur.com/maWB8.png)](https://i.stack.imgur.com/maWB8.png)

Someone who has no business with the design, but has a loud voice is trying to suggest making the first line ("Your card is now active!") the size of the second line and the second line the size of the first.

[![enter image description here](https://i.stack.imgur.com/Vq4TS.png)](https://i.stack.imgur.com/Vq4TS.png)

I'd like to be able to prove to this person, without stepping over my boundaries that this is incorrect, but I can't find a source as to why. 

Please remember, this is the very first thing a user will see. Besides the design not looking good and this certainly not working for mobile, is there any article anywhere that can back up my claims?