Yes, observation is science but observation alone is not science.
I appreciate that you have considered all of the fossil and DNA evidence that purports to make a valid claim for the Theory of Evolution being both a fact and a theory….but, again, and I cannot stress this enough….if your conclusion is not based on conclusions via the scientific method, the even as outrageous as it may seem to you, your conclusions are an assumption. You simply cannot demonstrate scientifically that what you believe to be true is, in reality, true. That’s the point. You have formed a conclusion but it is not a scientific one.
So in order to use the scientific method we must make no assumptions? Not true. If it were so, then the only things we could approach scientifically would be things we knew perfectly. ie. Nothing.
Science only requires that we are willing to change our assumptions if the are falsified by future data. I.e. Snakes in the Devonian
Of course you can make assumptions. That's not my contention. My contention is that you need to be able to test those assumptions using the scientific method.
Regardless of how much the natural world "suggests" that snakes evolved from lizards, the absence of a proper scientific analysis (using the scientific method) renders whatever you deduce from the "suggestions" as nothing more than an assumption. Now, it may be a very very strong assumption but it is an assumption just the same….and whatever conclusion you draw cannot be deemed scientific.