Yep, I was surprised I about the response time too. I'm not sure what's going on under the hood, maybe OpenAI did something with the stream output that causes the slowness.
Perhaps it is simply a way to limit the number of queries? If you force people to wait 10s for an answer they aren't writing new questions all the time.
For me it's been consistently the case that after 2-3 messages, the animation would start to visibly lag, and eventually (on 3rd or 4th reply) slow to a halt, sometimes mid-sentence, completely bricking the session. It's been like this since ChatGPT was first opened to public. I initially assumed it's just the usual case of a bloated SPA, but now I think maybe I'm being throttled on purpose?