An argument against the "You should be the difference amongst 10 players"

Okay, for quite a while I've seen an argument that goes like this, varying in every re-telling but keeping the same message, most of you will probably be familiar with it. I will retell the argument to make it easier to break down (Don't worry, I won't be changing the message at all).

So suppose there are 10 players, 5 on the enemy team 5 on your team, for you to rank up you have to be the difference.

Let's say we represent the enemy team's skill with numbers:

The enemy team:

1+1+1+1+1 = 5

And then it (the argument) would proceed to say, now you have your team:

1+1+1+1 (4 Players excluding yourself) And then you have to be the difference, so if the enemy team is 1+1+1+1+1 And your team is 1+1+1+1 but you're +2 then you should win, because you're the difference.

The final part goes on to say that there will be the game which is unwinnable but if you stay consistent you will rank up since you're always making a difference.

This whole argument has some good points but it's false.

1. It will never be 1+1+1+1+1, It will be something more like 0.5+2+0.3+1+0.2

2. It implies most of the time everyone will be around the same skill level

3. It excludes games with afks, trolls, etc... These games happen more than you'd think, you can't rule them out.

If your team is 0.5+0.5+0.5+0.5+2 But their's is 1+1+1+1+1 Then guess who's in favour to win? them.

Some of you will say, that's why you have to be + 3 or +4

To which I reply: Yes it's true, you'll rank up if you're good enough, but if you belong in your rank, are maybe a few ranks higher, there's a good chance you'll have an extremely hard time ranking up, which is why I get annoyed when people use this argument.

These days you can't be +2 you have to be + 3 or +4, you have to be better than the rank you're trying to achieve to even have a hope of achieving it, if you're trying to achieve the rank you deserve then it won't come easily.

No tl;dr because I'm only interested in discussion.

Have an argument against my argument? Please post it because if I'm wrong here I'd like to delete the thread.