No doubt, but that’s assuming you can control the image that gets loaded, then control it’s sizing and placement. If using the CMS, you cannot determine which size gets loaded on the page because you aren’t actually placing the image on the page. You’re using a block, that all items will use. All images must be the exact same, or you’ll get different results.
You’re setting a placeholder, not the actual image. Also, if you lock the image size with a Div, that will work, but now you’re not using responsiveness. It’s stuck in a pixel block, in a set location on the page.
Okay, let’s use percentages, or any other size… this is exactly what I’m talking about. Now you cannot predict the “actual” size or placement of the image. One visitor has 3840 monitor, the next user has 1280. “How can the image delivered be the same without losing resolution - if it’s a JPG?” No way that’s happening.
Not to mention, in the CMS, I may have an image with 1980 width. And I’m using a full 100vh header. If that user has a 3840 monitor and loads my page, how will the JPG not lose resolution?? It’s guaranteed to blur because it’s being scaled up.
Okay, let’s say we NEED to use JPG, we must add a very large photo and compress it. But it’s still not a guarantee the size of the image will fit the exact Div size, exactly in the spot we want, the way we want. You’ll get varying effects because it’s a JPG, when using the CMS – because we can’t control anything regarding the image after uploading it.
In Assets, there are a number of option to use - individually. I can use background image for one block, drop an image element just below it in another block, add percentages on another block, then use VW for another - all on the same page! You can’t do this using the CMS. They all need the same properties together.
Yet, the CMS is still fabulous and the best tool inside a web designer app on the planet, for the price and what you get. No doubt. But this is a little wrinkle, a small workaround for those special cases when each photo must be absolutely spot on.
Believe me I tried everything, going to different monitors, etc, etc. The best practice if you need, and I mean if you need to ensure the quality, location, everything, it’s best to use PNG in the CMS for important images. Not all, just the main ones.
It’s a long topic that takes a while to explain, but it’s something you can test to see … 
See ya.