I know why you're being sarcastic, but the Discord client DOES feel more responsive to me in daily usage. Especially if you're planning on clicking any links, which in Steam does a background API call to the Steam servers to check whether you should see the pointless redirection screen. This sometimes takes several seconds, and there's zero UI indication of what's going on. If you're impatient and you click the link several times, it will the open in multiple tabs at the same time.

Okay, the chat itself in Steam is pretty fast (unless you attempt to send an emote). The problem is, there's zero message delivery guarantees, and the client doesn't even care to inform you whether the message has been successfully sent. If you're on an unreliable internet connection, your best bet is to close and re-open the chat window to see whether the messages made it to the server in the mini chat log that shows the last 2-5 messages (that's the extent of the client's chat history feature by the way). It's an usability nightmare.

This isn't about how fast Discord is but about how bad of a job Valve is doing (I'm not even certain present tense applies here given that the chat client has essentially not received any major new features for like a decade).