Sorry I just saw this.
1) While the pitchers arm is in MER, his front leg should extend up by driving through the ground. Here is Sonny gray at FFS
And here he is in MER
See how he lands wjth a bent front leg, and then it's extended? This sends tons of energy up the chain into the arm.
2) yes. Reaching with the front leg hurts stride length. When a pitcher reaches out, he (typically) forces his hips to open early, which means he rotates off the back before he would early and loses a ton of energy.