Yay! They implemented the exchange today

There is a good description for skill which enhances the Soul's skill (for example Arthur's Absolute Monarchy), but could someone explain how the first one works? I see (++++) on HP weapon, but for Excalibur there's only "All allies' Wind ATK up" - Is it the same as for the other one and I should count + as 3%, meaning 12% in total? And what will increasing the skill level grant us? The same (0,5% per 1 lvl) as with your usual weapon? Finally, what of increasing the level of second skill?