Just a few thoughts-
Our public school does this, at least at the middle school, 5th-8th grades. We also have a pull-out program and live in a state with no gifted funding or mandates, so things may not apply.
Re: sports, here they begin after the "enrichment period," which is a time period immediately after school ends, lasts 50-60 min. All kids are encouraged to stay for the enrichment period, it is when teachers are available for extra help, the computer room and library are open, there are study halls available for those who just want to do homework, or one can choose intramural sports or going to the fitness center, various clubs, etc. So while math club (the only math enrichment here) and other clubs geared toward GT kids meet then, so do all the other activities.
Re: transportation, there are scheduled "late buses," a limited run schedule to take kids home after the enrichment period. Many kids stay after enrichment for athletic practice which generally lasts till 5ish when pickups are easier by parents.
While I have heard good things about the math club, and the school refuses any acceleration, etc in this area, our kids have not wanted to join. DD has joined another "academic" geared afterschool club, though, and loves it- suspect it is mostly related to the subject matter being of more interest to her.
Overall, I agree that this sort of plan is lame, but recognize that our school is inflexible, refuses acceleration, etc, and budgets are tight now; while I don't like it, I am glad that at least some opportunities exist. Better than nothing, if you will.
ETA: I suspect most of these decisions stem from the need to provide equal opportunities for all- since we have no funding for GT. To provide any perceived extras to any subset of kids would be taboo here- even the GT pullouts are balanced by "push-ins" where the GT teacher does units in the regular classroom involving all the kids.
But a lot of classes after school are not school based so may be during the enrichment period.
I can see it might be the best you can get but doing hours of underchallenging work followed by one hour challenging stuff doesn't seem fair. Can the be excused normal maths if they do more challenging stuff in the enrichment club? She could do her homework and balance things out a bit.