The thing that immediately comes to my mind is that many of these premed classes are tough.
Just to give one example, my younger daughter ended up as a biology major in university. The required classes overlapped a lot with premed classes. Freshman year she took an introductory biology course which was intended specifically for biology majors. The course was full of premed students. Many, probably most, of these premed students were academically very strong. The class average on the first midterm was 45% (she did somewhat better).
I took this as the professor doing a favor for the premed students. Specifically, the professor was making the point that premed classes were going to be tough, most of the premed students were never going to make it to medical school, and most of the premed students in the class would need to either work harder in the class, or find a different career path, or both. The sooner the students learned this lesson the more time they would have to adjust.
The issue that I see is that you are likely to be a stronger student in a year or two or three. It is not obvious to me that taking premed classes when you are still a high school student is the way to maximize your chances of getting the grades necessary to help your acceptance to medical school.
And when you apply to medical schools, you will need to report the grades on all college / university classes that you have taken, even the ones that you took while you are still a high school student.
I do not know how you can judge how tough you will find the university premed classes until you have taken a few. Also, which classes any particular student finds tough might vary from student to student. As an example, I know someone who was a pre-vet student (the required classes are the same) who looked upon any required or recommended math and physics classes as what you take to pull up your GPA to offset lower grades in the tougher classes such as organic chemistry. Not all premed students think of math and physics as the classes that they want to take to pull up their GPA.
Mostly however, I think that caution is in order. This might be a wordy and/or detailed was of agreeing with @thumper1’s question: