It's not about GPT-3 or GPT-4 per se. It's about the rate of progress and the development of Theory of Mind.
GPT-4 plays ~1400 level chess having never been taught the rules of the game explicitly (except for potentially reading them on one of it's ingested webpages)
I would actually assume there is something more powerful than ChatGPT-4 at work helping the US military right now. Likewise for Russia.
There's even a possibly that's the reason the conflict is dragging on so long.
I've never got any impression either side is about to win at all. And yes, there are plenty of wars historically (and even recently, e.g. the Syrian civil war) that have dragged on for many many years. But Putin would never have launched the attack against Ukraine if he thought things would be where they are now.
How far off are we from a military-trained AI that could make that sort of prediction accurately?