I really like the new editor but I quite confused about the 'publish changes' dialogue. The first thing I want to do after editing is to have a preview. I would like to have a preview button next to publish. The publish dialogue itself has a confusing layout. Two button on top with 'resume' and 'publish', the edit comment area in the centre and 'preview' and 'review' at the bottom. 'Resume' is nothing else than closing the dialog, normally called 'cancel'. This can also be achieved with an X on the right top like in a normal dialogue. The UXD team has to decide if the want button on top or on the button of the dialogue, splitting the up is strange. The first time I opened this dialogue I didn't find the preview button because there is the edit summary beneath the 'resume' and 'publish' buttons and I didn't expect more button below the summary. The same applies to the 'Review your changes dialogue'. I think publish without preview shouldn't be so easy because editing the source code is always error prone.
Topic on Talk:2017 wikitext editor/Flow
Yes this is a common complaint and tracked in https://phabricator.wikimedia.org/T44138
I think that the team agrees with you that this dialog needs some work. It was designed originally for the visual editor, where some things, especially the (non-)use of page previewing, are significantly different.
We can't use "Cancel" for the "Resume editing" button, because it makes people afraid that their changes will be lost (i.e., "Cancel the whole edit and discard all my work" rather than "Let me make one more change before I save my changes").
I don't think that any of the boxes in the visual editor have an (X) in the corner. The style documentation begins at OOUI. I believe that one of its sub-pages explains which buttons belong at the top (generally, the most commonly used ones) and which belong underneath.