Haven't seen the latest season yet, waiting for netflix, but based on my experience of season 1, I don't think the show ever seemed too fussed with canon, unless you're gripe is not with the change in the story but something else..?
On that note, I mean it's not confirmed, but hypothetically, assuming Slade is the one to kill Jason, considering the nature of the show, it being, Dicks show, with characters and their stories revolving around him, then the show runners changing Jasons death to be at Slades hand would fit their ideal.
Jason is a side character for Bruce? Bruces adversary Joker kills him.
Jason is a side character for Dick? Dicks adversary Deathstroke kills him.