A few possible ideas for swain balance.
Change the passive to increase the base damage of his basic abilities by .25% for each stack he holds along side the heal.
Once at 5 stacks his soul fragment heal beyond the 5th stack is increased by 50%.
Make the passive into a per target cooldown rather than a 1 use static cooldown.
Allow for further stacks beyond 5 to be acquired and when swain activates his ultimate he gains AP based on how many stacks he had.
Remove the unit collision on his Q.
Make the explosion timer on his W 1.25 instead of 1.5.
Remove the healing cap on his ultimate and increase the ratio on the heal to about 26%.
Finally, while in ultimate form swain automatically activates his passive on a valid target without the need for the player to click.
Seems swain is in abit of a bad spot and I started thinking of ways his kit could be improved while watching videos of him. Couldn't hurt to share some of those ideas.