Okay, I will be blunt and not apologize, but I won't intend to offend, so bear with me.
Yes, you are very incorrect, the game as it is now, is exceedingly hard to solo carry, and the more members of your team that contribute, the higher your chances of winning. If top laner dies once, its time to gank when he gets back to even out the lane. If enemy ganks mid, return the favor to keep it even.
Yes, its very hard to do, but it results in higher winrates for the most part. The issue with repeatedly ganking lanes that are ahead, is that after the enemy is on a 3 death streak, they lose gold value when you kill them. Plus, a lane that is ahead, will generally stay ahead, so there is no need to keep babysitting them. 20 year olds don't need a babysitter, only the 0-12 year olds. Think of it like that.
Just remember, a team with 1 really fed person with 4 behind teammates vs a team with 5 even players, who has the better chances?