Huh? If refs miss a penalty call then any other infraction in the game should also not be a penalty?
1 - Hartman on Draisaitl should have been called a tripping penalty, ref let it go, figured he was kicking at the puck....that said, I thought they changed the rules years ago where even you attempt to get the puck (with your stick for example) and you get the puck first and still trip a guy...still a penalty. So yes, should have been a penalty......slewfoot? Not a chance. There is almost no similarity between this an a slewfoot other than the foot being involved. Slewfoots are taken seriously for a reason....much more dangerous than this play.
2 - Yes, McDavid should have been penalized for that. The comments that it couldn't have been intentional because he was looking the other way are simply willful ignorance. He could have some of the worse peripheral vision in the world and still be able to see him. That said, I don't know if it was intentional or not, but looked like it to me if I had to choose. He saw the guy coming, he initially tucked his arm a bit as if to squeeze by and then popped his elbow up a bit to get a shot in. Nothing really major there, but sneaking/dirty play. I wouldn't suggest it's anything more than a 2 min penalty though. Unfortunate the player left the game over it.
3 - The comments about McDavid taking more punishment than any other player in the history of the game are also dumb. Firstly dumb because it seems to be an excuse to allow the sneaky little shots. Look, I don't knock McDavid for doing it, players do little stuff like this, don't kill him for it, but call it for what it is. I don't doubt that McDavid takes a ton of punishment, but that's because he's a great player, they all take a ton. The more it seems to impact your game, the more you'll get as well.