My questions is about the basic ogre CR calculation of the monster manual, which doesn't make senses to me. I tried to make a concept of an "armored ogre" with chain mail and pikes (AC 16 and 15 (2d10+4) damage) . The problems comes when I recalculate it CR and it's exactly 2, just like the ogre, that seems odd to me, it's a deadlier encounter!. so I tried to calculate the base ogre CR.

I must be missing something, the ogre doesn't have special defense or something when I calc his CR with the Dungeon master's guide I end with a result of 1.

If we calc his defensive rating we start with a 1/2 CR for HP, but his AC is 2 points lower than the suggested AC, so his effective defensive rating is 1/4

His damage rating CR is 1, but he has 2 points more attack than the suggested for his CR, so he has an effective attack CR of 2.

We end with an average between 1/2 and 1, so his final CR is 1. What am I missing?