Ah right on cue - weren't you hysterically bleating not long ago that everyone who opposes inclusion of trans athletes in female sports was transphobic?
Anyway, to your abc -
a) It doesn't matter if there are enough trans athletes - once upon a time there weren't any female athletes, and then there were. There were no paralympic athletes and then there were. You don't go from 0-100 overnight and the way demographics are changing the trans athlete wedge will only grow thicker in the years to come.
b) It isn't a token gesture - it's a sporting body creating a space for trans athletes to compete whilst maintaining the integrity and competition in female athlete spaces. This open category hasn't come out of a vacuum - we've seen over the years the records, spaces been taken away from female athletes, so this is a result of that. You may not think it's the best solution, but for female athletes, it most certainly is.
c) They're not men and women in the sporting arena though - they are biological men and biological women and that comes with distinct and inherent differences in sport.