This card is supposed to activate a subtle effect (generally weaker then what a card can do)Because it is an immaterial repeatable ability.
UP
For , considering it's healing ability (Heal, Bond, Shard) and the rushing ability, I guess it could heal 3 HP per turn, but definitely not more than that. Remember this card already heals (unupped) and is stackable.
For , mid-game to late-game condition is considered when using the unupped version. By that time, decent amount of defence can be set up (Hope/Sanc/Miracle in hand) and the skill can overcome lobotomize. For upped version it allows you to set up faster, so I don't see why it is UP.
For , again I think I could make it deal 3 damage at max.
Some relevant comparisons. Draw your own conclusions.
Shard of Gratitude (Life) vs Potential (Life)
SoG: 1 card + Life Mark + 5
+ 0
per turn -> Regenerate 5
Potential: 1 card + Life Mark + Casting restrictions + 3
+ 1
per turn -> Regenerate 3
Luciferin vs Potential (Light)
Luciferin: 1 card + 2
+ 0
per usage -> All creatures without an active ability gain Biolum and you heal 10
Potential: 1 card + Light Mark + Casting restrictions + 3
+ 1
per usage -> Target creature gains Biolum
Shard of Void (Darkness) vs Potential (Aether)
SoV: 1 card + Darkness Mark + 5
+ 0
per turn -> 3 max hp damage
Potential: 1 card + Aether Mark + Casting restrictions + 3
+ 1
per turn -> 3 Spell damage