Make Shulk's attacks less laggy would be a huge start. Also, while Shulk's Monado Arts do modify his pros and cons, some of them just don't bring enough fire to be efficient.
For an example, the Smash Monado Art may increase the knockback of Shulk's attacks at the expense of lowering the damage that he deals, but even with the knockback boost, Shulk still can't KO his opponents until they reach the higher damage percentages, unless he happens to get lucky with Vision. Even then, you're making Shulk more vulnerable to getting KO'd early, as his knockback resistance is weaker, and he's even more vulnerable to shield-grabs, since Smash also weakens Shulk's shield damage strength.
Last up, Vision's counterattack is quite slow to startup. If you block an attack like Koopa Meteor, the opponent can easily grab a ledge "before" Vision's counterattack strikes, causing the counterattack to completely miss the target. Most other counters strike much quicker than Vision (this includes even Palutena's Counter).