Using the title "Dr." depends on the setting. It is appropriate to identify yourself as an expert (using the title of "Dr.") depending on that setting. This includes the clinical setting for MDs, research setting for science PhDs, classroom setting for humanities PhDs, etc.
Also, not all doctorates are created the same. Some are very difficult to earn and they qualify you as an expert in that field. Others are less rigorous and border on "pay to play."
One tell-tale sign of the difference is funding. Most respectable science and humanities PhDs are fully funded with a living stipend provided for by the university. On the other hand, the less reputable doctorates are funded by the student and usually have a lower bar of entry, less supervision, no general examinations, etc.
The difference is huge and I honestly think the latter should not be allowed to operate.
Doctorates geared towards "executives" and "professionals" tend to be less rigorous and are therefore less respected, which includes many (all?) nursing doctorates as well as some/many (but not all) education doctorates, although this does not apply across the board. Overall, I would never consider a professional doctorate or an EdD at the same level as the standard PhD, although I think the title "Dr." is still appropriate in the right setting, as long as it is not a "pay to play" degree.
In my view, a psychology research PhD that is fully funded by a respectable university is more respectable than a PsyD, a professional doctorate, that the student pays for.
So, it's really hard to generalize here.