We will revisit button customizability later, it is already doable in a theme component or a plugin if you must but think it is better just to live with the change for a bit.
The GIANT issue with the header button is that it is of zero use once you learned how to do headers. Typing # test is way easier than reaching to the mouse and clicking header. The only real purpose the button served in the past was discoverability.
Anyway we can talk about this again in a month or two after some real world use cases ideally of paying customers come our way that really demonstrate how this is needed on a regular basis.