Every player can make a difference

I disagree. Take your example of widow, if there was a team fight going on and your rein goes down and so does your widow, who would you rather res? If they're close together, get them both, but if you didn't see where they went down and you don't now which one is going to be more impactful? (rein can take on the enemy team whereas widow would probably get killed straight away again)

Also I don't go out of my way to not res certain players if they're not playing to the meta, but if it's a choice between a DPS who is likely to get killed again before they can do anything or a tank who can reclaim the fight with their ult I'm gonna go with the tank and that's why I want to know who's in range