I think if there's one thingf you need to change about Suicide Squad, it's not the Joker. It's not the Enchantress. It's not the level of threat.
It's the music. The movie seemed to want to copy Guardians of the Galaxy and include a lot of popular songs, but they Guardians had a particular theme that tied into it's main character and gave the movie some identity. Squad just played whatever sounded nice without any thought to it.