Catalyst is more of a liability against scan Legends than a counter to them.

Catalyst's wall is supposed to be some sort of "counter" against Scan abilities, but it's ended up being more of a liability, very likely to get you killed in certain situations.

Seer's Ult will scan you through the wall, as will Crypto's Drone and Mad Maggie's passive https://routerlogin.uno/.

I've had several situations already where a Catalyst on my team has used the Ult in what seems like a useful manner, only to get absolutely beamed through it from enemies that I can no longer see.