No, It's not. If that's true why bother having a 10 point scale at all then. Just have 1 or 10. There can be no in between!
It's been generally accepted that the 100 point grading scale of school is how people think of the 10 point scale of video game reviews (school percentage grades divided by 10). 90+ = A, 80-89=B, 70-79=C or average effort, 60-69=D, 59 and below = F.
If you're ok with paying $60 plus DLC for C games, it's fine. Others wait until C scored games get discounted or simply avoid it. And that's fine too. Some people have limited gaming time and only want to fill their limited gaming time with games that are A or B quality.
Sometimes it's also best to wait for user reviews in the OP of the game on this forum or other places and not simply rely on industry reviews to form your opinion.