Think it's important to start by making a distinction between different groups of users.
- Someone who installed Wordpress at his/her web host and has no coding experience, just wants to have many buttons in the editor, like Word
- A developer building a website for a client, who wants to maybe restrict the ways his/her client can edit content

In both cases you might like to put the most-used buttons in front. But for different user groups different kinds of editors and button configurations are optimal.