Check how retail works.
After some research I fond that:
Absorb Light Souls - ID 393
Absorb Shadow Souls - ID 394
On SkillGRP both has reuse_delay=5.0
On Vanguard Open Source dist\game\data\stats\skills\00300-00399.xml they have <reuseDelay>2000</reuseDelay>.
The same reuse delay are active on the current Crusader test server.
Then, in this specific case, it's a datapack issue.