Lots of facts in science are not observable events. Just about all of geology is based on working out facts about the past that we cannot recreate. It is a fact that Hawaii formed a few million years ago, even though noone witnessed it. Same with astronomy. It is a fact that Pluto orbits the sun, yet noone has witnessed a full orbit. It is a fact that the craters on the moon were caused by meteors, yet noone observed them. It is a fact that stars form, burn and die in a certain way, yet noone has observed one do so. It is an inference from current states of stars and models.
Wouldn't evidence contrary to that inference be relevent?
Yes it would. But what evidence contrary to the inference would you be suggesting? Arguments such as "the eye seems to complex" are not contrary evidence. They are pointing out gaps in scientific knowledge, not scientific knowledge of gaps in evolution. Fact is we don't really know how the human eye develops in the embryo yet so it really isn't suprising that we wouldn't understand how such development itself could evolve. This is due to a lack of current knowledge and technology. Only when such knowledge and technology becomes better will answering the question "how did the eye evolve" become really possible.
But more to your argument about the Cambrian record--it too rests on a large assumption. I'll let you figure out what it is.
The cambrian strata in the grand canyon are labelled. If you found a mammal fossil noone would be able to deny it.
It's really not that hard.