Rakan's passive shield does not in any way benefit from "increased shielding and healing" items or Windspeaker's Blessing. If you buy any of them or use Windspeaker's Blessing on Rakan you'll find that his shield isn't increased from those effects. I'm not entirely sure what the issue is, but it could be an aspect of why his winrate is currently so low!
If I am not mistaken, it says heals and shields on allies.
I could very well be wrong or maybe I am thinking of an item that says that specifically but I believe that it refers to allies, not itself. Would you like it if Yasuo's passive shield or Malphite's ... W is it?... or Poppy's buckler increased their shielding? It is with other allies, not self.
EDIT: I was thinking of Ardent Censer attack speed increase and Athene's Unholy Grail. I will have to say it is due to the word "power" -- 10% increase shield and heal power probably has the implication it has to be an active ability.
What make you believe that it was not increased? By looking at Rakan's tooltip shield number (I never played Rakan, so I assume his passive show the amount of shield he receives). Or by actually seeing the shield amount on yourself?
I haven't tested it on Rakan yet, however I have tested this on Malphites passive and the shield from the Relic shield Quest. Both do not get increased by Windspeaker's, Redemption etc. I don't know if this is intentional or not but at least it's consitent.
