Onoki has no way of using jinton on hiruzen as it takes prep time and hiruzen simply has to throw one shuriken and clone them to disrupt him from using it. And lets not forget, that in every battle oonoki is in he ALWAYS suffers from back pain (this is cannon), so in that moment of weakness, hiruzen will strike and kill onoki.
Also, rock golems will get crushed by enma. And even if onoki somehow weighs down enma, this will most likely end up being worst for onoki as hiruzen doesn't have to physically hold enma to attack with him, enma is capable of controlling himself, so by onoki making him heavier it just allows enma to strike him with more force.
Hiruzen's lightning stream should be enough. All five elements are not even needed for this.