But what if none of them know which of them expanded first? There might be several forces colonising the galaxy, and all keeping extremely quiet so that they don't get noticed and destroyed by and older civilisation. Thus no need for a great filter, and even if UFAI were common we wouldn't observe it colonising the galaxy.

This requires either:

• Interstellar travel is much slower than seems to be possible (a non-trivial fraction of the speed of light)
• "Colonizing" or rather fully exploiting the resources of a star system or other object takes a long time and is also for a long time more economical than just expanding again to grab the low hanging fruit a few light years away.
• That no civilization in our galaxy has a head start long enough to win. My best estimate is that a few hundred thousand years before any other is more than enough.

It seems much likelier that we are alone in the galaxy. Either civilizations are pretty rare or we are the oldest one. If the latter is true this seems anthropic evidence in favour of the simulation hypothesis.

Your argument works much better on a much larger scale, for example it does take millions of years for light to travel between galaxies.

But what if none of them know which of them expanded first? There might be several forces colonising the Virgo Supercluster, and all keeping extremely quiet so that they don't get noticed and destroyed by and older civilisation. Thus no need for a great filter, and even if UFAI were common we wouldn't observe it colonising the Virgo Supercluster.

~110 or ~200 million year head start on intelligent civilization building life on a Earth like planet still doesn't seem obviously unlikely.

But what if none of them know which of them expanded first? There might be several forces colonising the visible universe, and all keeping extremely quiet so that they don't get noticed and destroyed by and older civilisation. Thus no need for a great filter, and even if UFAI were common we wouldn't observe it colonising the visible universe.

This is almost certainly true, but at these scales the speed limit of the universe is a potent ally. By the time anyone notices you are doing anything many hundreds of millions of years of you already doing whatever you wanted to do with the local matter have passed.

Also see metric expansion of space. The farther away an object is, the faster it recedes from us.