Harmony - Troop Symmetry

If someone hasn't seen something, it doesn't mean it doesn't exist.

Those two sentences refer to different things, not to the same skill.

The second one means: either we take it into account or we don't.
(I don't have time to explain further)

Added 3 minutes later

But isn't it true that "true luck" gives 100% for both attack and counter-attack?

It learns at the expense of a decrease in other combat parameters.
That's why I wrote: "I haven't seen the skill." The skill is evaluated not without taking into account what it learns through.
(and also what other hero skills learn through).