Stick it out with the competitive HS. Encourage your student to take rigorous classes senior year, as college look at that. The only senior year grades colleges consider are first semester (and that’s only for colleges with deadlines after 1/1). Encourage your student to do their very very best with grades junior year. That end of year junior GPA and class rank are what the colleges see in your apps, especially if your student does rolling admission, EA, and ED.
Also, it’s not just about grades. What else is your student passionate about? Hopefully your student is involved in activities, and shows passion for that activity. For example, if your student is a “coder”, they should get more involved in that, such as teach coding to middle schoolers every Saturday, help senior citizens with FB etc. Same thing relates to sports. Don’t just play a sport. Teach the sport. Volunteer Coach a sport. Ref a sport. You don’t have to do 15 different things, but be passionate and show development in a few.