Is Attack Boost broken?

Edit: that was actually raw, not true raw so numbers were wrong.

Equipped level 5 Attack Boost and realized stats are actually ~~cumulative~~
So it's not attack +9 and 4% at level 5, but attack +3 +5 +7 +8 +9 + 4%

For example playing CB, when using Hard Bone Strongarm and it's 828 raw attack, I get 894:
828 + 3 + 5 + 7 + 8 + 9 = 860 + 4% = 894