The weaknesses you cite here are not weaknesses... these are basic properties that every character in the game has to deal with - high starting strings happen to usually have strong properties, launchers are punishable, overhead/low starters are for the most part non-existent or weak.
Saying a tool isn't very strong because it comes from a high, particularly when a character has some of the best mids (staggerable at that) in the game, is very silly. Nor is the fact that your stated b24 situation plays by basic strike/throw rules make it any less real.
Cassie does not lose to Erron or Jade, and all the strong Erron/Jade players I know agree. Jade's zoning really isn't oppressive enough to outweigh the fact that Cassie beats her any part of the screen besides full screen with way better neutral and damage. Cassie has better neutral than Erron, and if you are having trouble getting into footsie range/getting zoned out by Erron, then its a you issue, not a matchup issue.
She's a really strong well rounded character, the fact that she may have to be the one to approach in certain matchups doesn't mean she all of a sudden loses the matchup.