Man , i miss the days when phinn was banned or picked hehehe
Now everytime i see someone pick him in 3v3 or 5v5 i laugh , he is getting destroyed by everyone .
I think the way to balance him is by adding two things :
make him strong against breaking point and dragons eye , he shouldnt be a free stacks , make the items slowly building stacks against him like 2 hits to build one stack instead of 1.
add to his B anti burn damage , when he activates his B he should provide fortified health and remove any burn damage (mortal wounds) , make him useful against this spellfire and poisonshiv meta .
You can reduce his damage , i dont care , just make his utility better for the current meta , he cant do anything against a lot of heroes .