How does a half-duplex medium (e.g. Wi-Fi) affect simultaneous up/down transfer in practice?

I'm sorry if this question is confusing, let me clarify what I mean.

So, Wi-Fi is half-duplex. This means it can either transmit or receive, but not both at the same time.

So let's say an AP and a client are connected at a theoretical link (PHY) of 1200 mbps up and 1200 mbps down.

In the real world, this means you'd see roughly 600 mbps download and 600 mbps upload. But if you try both at the same time, you'll only get 300 mbps down and 300 mbps up because it's half-duplex.

Am I correct in my thinking so far?

Okay, now let's say you have an asymmetrical internet connection. Let's assume you get 500 mbps down and 50 mbps up to your ISP, and you have the same 1200 mbps up and 1200 mbps down theoretical Wi-Fi links.

You try to run simultaneous up and down tests. What should you see?

1. The up and down each get cut in half (so you get 250 mbps up and 25 mbps down)
2. Only one gets cut in half (upload is 25 mbps, download is full 500 mbps or vice versa)
3. You get the full 500 mbps up and 50 mbps at the same time because it's below what the Wi-Fi link can support (600 mbps combined up and down).

Sorry if it's confusing, I'm just trying to understand Wi-Fi better and make sense of some speed tests.