I feel that some of your explanations are a bit off.

The way I see it, the philosophy of this build is to "reduce cdr as much as possible so that I can use my shield more to tank for my teammates", but any team worth their salt is going to ignore you and go straight for your carries.

Yeah, you can use your stun more than once in a teamfight, but there's only so long you can stun them until they burst down your carries. By getting Fountain as a late-game item, you won't be able to easily save your team from death, or increase their durability in a teamfight.

"She doesn't have the Vanguard of Ardan, the heal of Adagio...the tankiness of Phinn...she is made to deal the lowest damage"? Firstly, what she does offer is an impressive array of lockdown and tankiness. Remember, her heroic perk makes her a bane to all carries so as long you're actively stunning, which is why I disagree with your "playing passively" tactic.
Second, she is MADE to deal the lowest damage, because she doesn't NEED to deal any. Just her skillset alone is more than enough to prove a hassle for enemies. Catherine doesn't bring power through damage. She does it through lockdown.