That comparison is also misleading because Opus 4.6 was probably not Anthropic's frontier model.
We got the first news about Mythos in March, so it is likely that it was already close to ready by the time Opus 4.6 was released.
So the actual gap is the time elapsed between March (or April for the official announcement) and whenever Chinese models can match Mythos.
The post-training process of a model that size is months, though it "works" before that. It is a big chunky model before it's released to the world and probably does some amazing things, sometimes...but, it wasn't done (else why wouldn't they release it and soundly trounce their competitors). I would assume that Chinese AI companies have a pipeline and what we see is a couple/few months behind their newest model, as well. Like, the new base model is cooked, but they're still plating it for service.
Why would Anthropic get the benefit of pre-release models counting toward their lead, if nobody else gets to count their pre-release models?