You're focusing on just lineman. I'd fully agree that o-line and d-line are encouraged to have unhealthy habits. Yes, there have been football players who have died of heart attacks. Often, they are lineman and it's often the result of heat exhaustion and/or a previously un-diagnosed heart condition. The rest of the position players don't follow those patterns. They're encouraged to be as physically fit as they can be. With lineman aside, you won't find overweight, out of shape football players...at least not at any level of success. The argument about putting an obese 8th grader on football vs PE is likely to be true, but not because of any physical activity matter. It's because guess where that obese kid is going to be put on the football team? The o or d line, which we both agree does encourage poor health habits. However, if the coach were to say (which sadly doesn't happen enough), "hey kid, you can be a linebacker or running back", I'd bet that kid gets in better shape than if he had done PE.
On the PE topic, I suppose that you're technically accurate that if everyone were forced to do 45 minutes of jumping jacks, push ups and air squats you would have active kids. Though I'd suspect the same kid who is picked last is also going to be the one who doesn't want to do those activities anyway. I know that at my kids school, it's actually a bit of a mix. It's not all "pick 'em" games and it's not all jumping jacks (for example). It's both. I'm good with that.