The id in html is used to generate the trans-unit resname, not the ID
That seems like correct behavior for xliff.
It is pretty rare that all elements in an html have IDs, so we would end up with a mixture of generated + from-the-html IDs
And generating IDs can't be avoided because certain items in HTML can't have IDs.
For example the attributes (area, alt, label, prompt, title, summary) are all localizable, generate separate text units, and don't have IDs.
I didn't play much (if at all) with OmegaT, but resname should also be visible there, no?
It is a pretty important xliff attribute.