Thanks for your feedback. I agree with you in principle. However, the current use case is that images are only allowed within <fig> elements which makes them indeed children of another block element. "Naked" images like icons are currently not used. Therefore I think changing the default behavior for the display of images from "inline" to "block" is a valid solution.
And even if our customer is moving in the direction of using standard DITA instead of their customized DITA, we will have to keep this behavior because of the legacy DITA documentation that would break if we change the default behavior.