Is it a good idea to send pre-submission inquiries to multiple journals to accelerate the publication process? or do we have to wait for the editors' response to a pre-sub before sending another one?
You should look at this question from the point of view of editors. Most of them do this work in addition to their usual work as researchers. Each inqiery causes additional work. In the worst case, a tsunami of such inquiries (if every researcher would send it to several journals at the same time) could lead to a collapse of the system. See also:
Thank you, Dr. Wolfgang. I agree with your response.
By multiple, I meant more than one. For example, if a pre-submission inquiry is taking too long to be processed, is it possible to send another one to a different journal? I understand that it's preferred to send one at a time in order not to waste the editor's efforts.
I think it depends on what is your pre-submission enquiry like. Is it very short or very long? If it is very short, they are more likely to respond. If it is a whole article, most editors are discouraged if it is too long like that because they might have lots of other work, unfortunately.
It also depends a lot on which journal and editor. Some will have time. Others might be too busy.