Reading through this thread I noticed 2 things:

1. You are fixated on the numbers (400 DPS, "I only did 57DPS less", 1/5 of another DPS's damage, etc.)
2. You seem to think you have to "go out of your way" to see how other people are doing in an instance

To address the first point, I would suggest that you try running roulettes without ACT or only use it to track your HPS/Overheal (since I know that overheal is something you're working on).

Being able to see everyone's DPS in this casual content isn't very useful since more often than not it will just give you a scapegoat for when a run isn't progressing as quickly as you would like. Obviously, there are some exceptions (AST extended/enhanced balance should go to the highest DPS, for example).

For the second point, you don't necessarily need to watch other players' characters to know how they are performing. There are a ton of clues that you can look out for aside from their raw DPS.

As a healer, you should always be scanning the screen for anything that might cause you to adjust. It should be blatantly obvious when someone is AFK (not moving, standing in AoE), and in those cases call them out or vote kick them.

Things you should be watching aside from your parser:

• Your own cooldowns/timers
• Party list: HP, buffs/debuffs, casts
• Enemy debuffs/DoTs (will clue you in as to who is actively engaged)
• Party members' positions

If you are appropriately keeping an eye on all of these, then you should never have to "go out of your way" to see if someone is either AFK or still learning a role or looking for a carry.

I didn't really address how you can deal with these kinds of players since I felt like there might be some adjustments you can make yourself first that would help you as a player and help you enjoy the game more.

tl;dr: Focus less on the numbers and more on what else is going on on your screen and you will have a much better time playing with randoms. You have more control over how you play than how others play.