Added damage to Herald of Thunder?

According to the wiki here
https://www.poewiki.net/wiki/Herald_of_Thunder
linking "added lightning damage" will add a portion of the lightning damage to buff which HoT applies to my attacks and spells.
Selecting the ALD support gem also has the little green checkmark next to it that suggests it is applicable to HoT.
Socketing the skill gem indeed reduces my mana as expected, but nothing else changes, neither via tooltip damage nor in PoB.
Is the wiki simply out of date again or is this a misunderstanding or a bug?
thanks in advance