Eh, considering he has to be within 7 meters of the enemy and land both shots to the head I’d say it’s not that problematic considering Reinhardt should also have teammates to help him survive (Zarya, Dva, Brigitte, Ana, Baptiste etc.) Widow can deal 300 damage from across the map with no falloff 
McCree is fine, there’s plenty of counterplay
This whole thread i don’t think anyone mentioned it (apologies if i did). But if you’re playing rein and a mccree is in flash range. You should try to predict the flash by flicking your shield up. Only time you shouldn’t do this is if you are expecting a shatter from enemy rein. If you expose your toes, he’s in.
I’m assuming Dva was played too. So what happened to her DM?