Crit enchant craft +5-+7%

Crit enchant craft +5-+7% - how does this work, because it costs a lot of runes.
if base crit of weapon is for example 7,5% - so enchant will add +7% to the base? so weapon will have base 14,5% crit chance?

No, just a general increase. Not sure why it's so tiny. Looks unintended.

So tiny skill node gives you e.g. 15% crit chance... and enchant on weapon which costs dozens of runes gives 5% ? Really... is this joke?

Skill tree nodes increase global crit chance, the enchant applies locally to the weapon's crit chance. Say, a weapons with 10% base crit chance and "7% increased Critical Strike Chance" enchant would result in 10.7% crit chance. For comparison, regular weapon suffixes provide from 10-14% increased Critical Strike Chance (Tier 6) to 35–38% increased Critical Strike Chance (Tier 1).