Yes, when using the stacked/list (i.e. not the masonry/columns layout) layout, this is the design of the theme to use the large image size, as each post is full width.
You could make the images smaller with some Additional CSS like so:
article .entry-figure img {
width: auto;
max-height: 300px;
}If the excerpt is missing, make sure that you have not selected the ‘Do not show: Excerpt’ option in Customize > Blog Options > Index, Archive and Search (see attached image below)
