ah yes, everything your opponent does seems lagless when you start your attack 5 frames later than them.
(in case you're curious, no attack cloud has is earlier than frame 5 with the exception of frame 4 Jab, which is identical to Bowser Jrs. Jab.
http://kuroganehammer.com/Smash4/Cloud )
Cloud suffers to anyone who has any sort of gimping game. With nearly straight vertical recovery, just about any character with access to a semi-strong back-air puts him out of business.
Beyond that, he severely suffers to the high-tiers. With Zero-Suit's insane combo game, speed and recovery, I'd think it'd be our worst Match-up, closely followed by Pikachu, for the same reasons. Sonic is definitely a tricky match-up, Fox and Mario as well, for their speed and combo potential, though the latter are more easily succumbed to Cloud's stage control strategy.
The problem everyone has with Cloud is how different he plays than most Sword characters. Unlike Marth's guerilla warfare, Ike's "Ganon with a sword" tactic and Roy's semi-combo style, Cloud plays a lot more like Melee Marth, with a high-risk, high-reward spacing game that relies completely on stage control. Clouds win when it's hard for you to get center stage. That's why we do well against projectile, and defensive characters. Remember, center stage is as far from the Blast Zone as you can get. A character that keeps Cloud on the edge, or in hitstun is a character that beats Cloud.