Support Casting is way too difficult

[Persain]

From WIKI

Spell Duration
Percent Guilds is the sole factor involved in spell duration. The higher the percent guilds, the longer a spell will last. This remains true until the maximum duration for that particular spell is reached.

Self Spells
For self spells, a higher percent guilds results in a greater:
Spell Duration
Chance of a Successful Cast

Offensive Spells
For offensive spells, a higher percent guilds results in a greater:
Spell Duration

So is a supporting spell a "self" or "offensive"?

offensive...you are casting "on" someone else.