What am I missing here?

And all "increase physical damage" are also applied after conversion. Not sure about increased attack damage, is it applied before or after conversion?

Added extra damage happens before any multipliers are done to prevent you from double dipping on them. Getting 21% extra chaos from your multiplied phys / ele and then adding any chaos multipliers on top would get really nutty really fast.

21% of damage before all modifiers!!! If all your modifiers increase elemental damage, chaos damage doesnt get benefit from them!

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I believe damage calc for attacks has the following order:

Start with base damage on weapon. Flat and % damage increases on your weapon are factored into the base damage.

Add any flat damage from sources like rings or gloves.

Multiply the base damage by the base damage multiplier of your skill gem

Perform damage type conversions

Add all of your "gain as extra mods"

Apply all of the relevant %dmg increases. Notably, if you have fire/cold/lightning/phys increases those won't affect the chaos DMG you added.

Apply any %dmg more modifiers.

Your life, don't worry i'll see myself out!

If you have other sources of % damage gain as x, then that nodes becomes less effective. Especially druid wolf, take out all the % damage gain as x nodes, and it should reflect closer to 21%

U just sold ur soul cheap

Im pretty sure that PoB will show you the real outcome of your dmg tooltip. My ele weskness and doedre‘s desire shows me just 2,6k chaos dmg but in path of building it tells me that ele weakness does way more than this(close to 380k i think because my ele weakness is lvl 42 and doedres itself takes the level by supported gem) . Its scales different in some indiscribable way.