The gunner passive has been broken since it got the update where it added 3% AP each passive stack.
So first the passive: https://cdn.discordapp.com/attachments/493760836829970432/578163323212660747/unknown.png
Visual display when active: https://cdn.discordapp.com/attachments/493760836829970432/578163395782508554/unknown.png (should be + 3% AP not + 3 AP)
Then I tried without any notable gear so my base stats were: https://cdn.discordapp.com/attachments/493760836829970432/578163117595295754/Client_tZpuiNT8X9.png (533AP and 533 Boss AP)
So with active passive I shoud have: when 1 stack = 549 AP and 609 Boss AP; when 2 stacks = 565 AP and 685 Boss AP; when 3 stacks = 581 AP and 761 Boss AP.
My results were:
-with 1 stack: https://cdn.discordapp.com/attachments/493760836829970432/578164894092754944/unknown.png which is 3 AP and 3 Boss AP less than it should be.
-with 2 stacks: https://cdn.discordapp.com/attachments/493760836829970432/578164828380725270/Client_hfi4etakxg.png which is 5 AP and 5 Boss AP less than it should be.
-with 3 stacks: https://cdn.discordapp.com/attachments/493760836829970432/578166828732514314/unknown.png which is 8 AP and 8 Boss AP less than it should be.
So as you can see no test is matching what it should be. It´s only getting worse the more gear you have and the more items you have that can proc as example the GC weapon.
(also as a NOTE: I calculated the results by adding 3% 6% and 9% to the base stats depending on stacks and NOT 3%; then 3% to the result from adding 3% and so on.)
If I forgot anything or if there is a question please let me know.