Hello @Goeller,
Thanks for writing in! Allow me to provide a little more context for why the post carousel on Ethos outputs images in the size that it does. As with most decisions related to resource usage in X, we have to carefully consider the options available to users and how they might set up that feature, along with how any of those number of settings might work responsively across a wide range of devices.
Regarding the post carousel for Ethos, not only do we have the input in the theme options allowing users to specify how many posts in total should appear in the carousel, users also have the option to specify how many posts should display at once for various screen sizes under the Post Carousel – Screen Display section. It is certainly a possibility that a user may wish to only display 2 or 3 posts at a time, even on larger screens, which would necessitate a larger graphic to ensure that it looks okay (especially on devices with a high pixel density display). Furthermore, at 549px, users can specify how many photos they would like to show, which will likely only be 1 at this point. Even at this breakpoint, you would want an image that were at least double the size of this pixel value potentially so that on high pixel density devices the image still appears crisp.
As you can see, there are numerous outcomes to take into account when developing a feature like this, and there is no way to know for certain how a user will set things up, so we opt to ensure that images will more than likely be large enough so that they look great across all devices and screen widths out of the box (as most users will more readily take issue with “poor” quality graphics than filesize). That being said, if you have ended up at a place where you know what your ultimate settings for this feature will be, you can certainly customize any views you wish via a child theme to further improve any output:
You may also want to look into an improved caching setup on your server, utilizing a CDN, et cetera, all of which are outlined to some extent in the article above. Site performance is always a bit of a moving target, and depends on many factors for different users in how they setup their site. Hopefully all of this has provided a bit more context on this situation and gives you a clear direction forward.
Cheers!