Giant's Blood Passive Bugged

Aside From Basic Attack all if your Skill Damages are Reduced.

The Math is not adding up right...
I'm expecting 847 DPS for leap slam instead I got 458 DPS which is almost 50% lower than expected?
And even lower than Single two-handed weapon which has 671 DPS???
(It's like the damage is divided by two? or averaged?)

Here are the photos for reference
https://imgur.com/a/zHuXy4S

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