Leg weights

Getting stronger over a long period of time will make you faster.
As for the athlete A/B, the answer can all depend. Three things can happen (I’ve actually seen all 3 happen, and that’s just in my high school alone)

  • the weaker athlete gets slower after improving their squat a lot
    -the weaker athlete gets faster after improving their squat
  • the weaker athlete’s speed is unaffected by improving their squat

It can vary, and how much of which option ends up happening, varies as well.

I’ve talked to someone who swore by heavy ATG squats, and talked to someone who said he’ll never squat again as long as he does track.

As for your 3 months, stick to the running and plyos.