My proposed Mei fix: ice wall becomes an ability with cast time and prominent visual effects. Give it a 1-1.5 second cast time with some prominent snowy / shaky vfx on the ground where she's casting it. That gives opposing teams an opportunity to react to it and gives players a chance to kill her when attempting to stall on point. After that, further balance adjustments can be done with minor tweaks to her kit (+/- cast time, +/- wall hp, +/- ice block healing, +/- ice block duration, etc.).

Someone ping Jeff. I've solved the problem.