I believe that you’re the one that doesn’t understand that comment.
Yes, even GMs doing bronze-to-GM challenges can’t win 100% of games.
Yes, some games can be much harder to win or carry than other games due to a variety of factors.
But those kinds of games are out of the ordinary; rare occurrences.
So yes, there are games you definitely can’t win, no matter how hard you try. So does that excuse your ability to climb to higher ranks?
NO!
Because the exact opposite is true as well; there are games you CAN’T LOSE!
Because those types of players that are ensuring you can’t win?
They can be on the enemy team as well!
And you know what’s funny?
Technically they’re more likely to be on the enemy team than on your team!
Because your team has 4 randoms and the enemy team has 5 randoms!
There are some games you can’t win and some games you can’t lose. The rest are up to your skill.
That’s the point of ranked play. It’s a test of ability over the course of lots of games, therefore you’re supposed to prove that you are consistently superior to other players of your current rank → therefore you rank up while the rest do not as they don’t win (as consistently) when you aren’t on their team.