Overwatch Woes

WARNING THIS IS A RANT

Okay, so I picked up the game two weeks ago and I am still fairly green, but as a longtime vet of Team Fortress 2, im used to team centric games.

My question for the Overwatch community:
Why do people buy a team-centric game, but refuse to actually play as a team?? Noone seems to pay attention to composition half the time, and it gets very old being mowed down on a payload match in less than 5 minutes because my team decided to play as 3 widow / 2 reaper, and I played reinhardt?

That being said, I really enjoy the pace of the game, and the breath of fresh air from COD type games.

Analysis:
Although players should adapt to each round, I have found that the following compositions seems to steam-roll the other team. (If everyone plays their role correctly)

Attack (capture)
Zarna - zenyatta - phara - lucio - junkrat - ?

Attack (payload)
Reinhardt - tracer - mercy - symmetra - mcCree - ?

Defense
(A tank of choice depending on map)
Junkrat - zennyata - symmetra - bastion - ?

Keep in mind, these are simply opinions, not facts, and definetly dont fit each and every situation.

Last but not least,
Hopefully Blizzard will continue to work on the play of the game system...

Watching a tank push his team to victory, or someone clearing a defense point at the last minute should be priority. Not the solo mcCree or Reaper that is going around picking off low health targets that arent even remotely near the combat zone... and god forbid the torbjorn that never left his turret the entire game and got a double or triple kill (once).