They only have an advantage if you start from the premise that sports need to be sex-segregated. What if we just let everyone compete, regardless of sex or gender, and found out through competition who the best were? If that's men sometimes, great! If it's women, also great! If it's transgender women, even more great! Transgender women only have an "unfair advantage" because we've decided in advance that there should be two separate classes of sports competition. Trans women athletes aren't the problem here. Sex-segregation in athletics is the problem.
P.S. Just because you’re bisexual, doesn’t mean you can’t also be a transphobe.