Imagine that 99.9999999999999% of the universe (and 100% of most galaxies) is under the control of strong AIs, and they expand at the speed of light. Observers such as us would live in the part of the universe not under their control and would see no evidence of strong AIs.

It is extremely unlikely that some non-terrestrial strong AI just happened to come into history in the exact same time that modern humans evolved, and is spreading throughout the universe at near the speed of light but just hasn't reached us yet.

The universe (not necessarily just the observable universe) is very big so I don't agree. It would be true if you wrote galaxy instead of universe.