High achieving students, like premeds, need to apply nuance, judgement and an overall view of their application and make a one dimensional decision when considering letters
Simply because a physician allows students to shadow all the time provides no indication whether he/she writes some standard letter or actually takes time to do an in depth evaluation. As I said before, the vast majority of typical premed students shadow a physician for 10-20 maybe 50-75 hours, following them around without much in depth interactions. These are the letters that really dont matter as they cant say much. So as a rule, the typical shadowing experience is not worth getting a letter over.
The theory of LOR/LOE is evaluate a student's academic abilities and characteristics; not what they did as much as what is behind how they did so.
So if an applicant has an in depth, constructive, lengthy, formal or some other connection with a physician, where the doctor is in a position to evaluate (not simply recommend) an applicant they me be worth something. As
@gyngyn said a PI is the typical example of this. I have many nontrads who work in a clinical setting and thus have physician letters as an employment supervisor.
In the case here, having a 1000 hours shadowing a physician and their team would suggest you may have a more structured and in depth connection with him/her. Furthermore, if the physician involved with rural medicine and that is your area of interest that you are expressing in your application, then it would valuable for that as well. But your situation is very atypical compared to the average shadowing student student.