They first need to buff normal Link significantly enough to at least match Toon Link's level.
The hate is because they are so similar in movesets that Toon Link is just regarded as a clone and people feel like he wastes a slot.
In reality Link is the one that is more like a clone; being worse than Toon Link.
If they could give him some more unique abilities and a new Final Smash, he could shine on his own and not be neglected as "just another clone";
Of course, some staples of Link need to stay as they are; the spin attack for instance is the signature move of all Links since ALTTP.
Some moves need to be changed up, like the bow, which could use (as mentioned before) fire and ice arrows - weaker arrows that affect the enemy differently. They could have even taken a note from Project M and how they added Samus' ability to switch beam types with a taunt. Even the boomerang could be changed to suit Toon Link more by having it be guided like in Phantom Hourglass.
Not to mention new moves need to be given to him altogether, for example a counter-attack which takes inspiration from Wind Waker's combat, or more items from WW and PT such as the Deku Leaf or Skull Hammer.
Finally, his Final Smash could be something along the lines of hopping on the King of Red Lions then flooding part of the stage.
He has potential to be more unique but unless Sakurai has implemented changes to make him less of a clone character and to justify his slot on the roster, the hate will always be there for poor little Toon Link.
Doesn't mean you have to pay attention to the haters though