Tyranitar Attack Grades
There's no way B/C and B/FB are equal grades. I love your rankings but that's just wrong. I have both and FB blows in comparison.
https://pokemongo.gamepress.gg/pokemon/248
Answers
Gamepress tends to give bonus points for having mixed type attack moves. You also have to consider the meta where Fire Blast is actually very useful against Blissey and Crunch is resisted by her.
Also keep in mind one bar offensive moves are commonly better than 3 bar offensive moves because , with a full 100 energy, youre spending less time waiting on the animations and CDs of 1 special attack than 3, which is more time that you can be spamming your quick attack and building more useable energy than spending it. Crunch is a high damage 3 bar move with STAB though. All in all, I would say they are about equal on offense, but as somebody else said gamepress's rankings are just as subjective as your own to an extent, so use your best judgment.