The new behaviour of "mark everything read" from T150045 does actually take more time for users, as they need to manually refresh the page afterwards. Even if this would be done automaticly it would propably take longer than just one request for marking as read and refreshing.

Also this still marks everything read, even changes new enough to not yet beeing shown. In combination with this issue, this makes it even more likely than before for users to accidentially mark changes as read without even noticing.