Only you, of course, can truly know how you want to proceed. Talking with your high school counselor and your folks or those that help guide you in your decision making are the best people to help you decide. But you asked… My general thoughts -
The main thing you know is that Harvard’s RD pool will also be exceptional. As @highschooldad1 mentioned It will be filled with folks deferred or possibly rejected by Princeton, Yale, Stanford et.al. It will not be a weaker pool filled with recruited athletes (though these athletes are still strong students) or overfilled with legacies. That Harvard RD pool is also an exceptional pool of applicants. Your stats are very good though not off the charts and because of that, imo, you would be a very strong candidate for Tufts RD pool. The risk you mention is foregoing a possible Harvard admission for more of a sure thing at Tufts EDII. I’m not sure you have to EDII.