Not true at all
You fucked up the xml of the skill or something else on clean version work perfect

I did not modify the skill XML.
Skill 1235 (Hydro Blast) is clean from the original Mobius Interlude pack.
Important detail:
• Damage to regular NPCs = normal (works correctly)
• Damage to other player = 1
• Damage to guard NPC = 1
• Other magic skills work correctly in PvP
So this does NOT look like broken XML or wrong power value.
It looks like a PvP-related calculation issue (possibly elemental interaction or PvP formula layer), because PvE damage is correct while PvP damage is always 1.
Tested on clean skill file without modifications.
Can you confirm if there is any known PvP/elemental interaction affecting Hydro Blast specifically in Interlude branch?