You are correct in that popular media does take those shortcuts, which for the uneducated masses becomes irrefutable fact. There are many things full of holes that are taught as complete fact. Having just finished an "environmental sciences" class, I nearly drove my professor nuts pointing out the holes in the textbook itself in the "Carbon emissions are causing Global Warming" theory. Nonetheless, Evolution still hasn't been proven.
Agreed that the DNA evidence is very persuasive, as are the surprisingly tiny number of fossils of a "human type creature." You'd think that as many years as that must have taken, we'd find more of them. But the few that are found, are persuasive.
Also the age of the fossils is in question. They simply go by the strata in many cases. Who is to say how thick the soil really and truly got in any given number of years? I don't buy it.
I'm not saying that all of this is WRONG. I do believe that Evolution is how things happened, and I do think the old stuff is incredibly old. I just don't think any of it has been proven beyond doubt enough to present it as fact rather than a theory or hypothesis. i.e. "This fossil humanoid is 20 million years old" If it's indeed that old, and mankind has been around that long, what on earth have they been doing for hundreds of thousands of years not to have left any more than a few bones? Or primitive paintings?
I will reiterate -- that evolution occurs (changes in the gene frequencies and heritable traits within a population over time) has been proven. How, exactly, the lines connect fossil forms to living forms is something that can't (at present) be proven, but is inferred by balancing evidence from multiple areas to weigh the most supported answer. Darwin wasn't the first to come up with the idea that populations change -- this was known by people who selectively-bred animals. His theory was that this same process, performed as a result of selection "by the hand of nature" and over a long enough time, could account for differences in species today that derived from a common ancestor. The observation of genetic change over time is the fact part. The proposal that this process can account for all species today because of common ancestry and changes through time is the theory part.
Fossilization is a rare event, considering the number of individuals of a given species that ever existed. Any individual which was consumed and digested in entirety will leave no fossil remains. Fossils are more likely to form in some environments than others. Species living at high densities are more likely to be represented in fossil layers than are species living at low densities -- though the La Brea Tar Pits provides an example in the opposite direction, being as trapped prey attracted a disproportionate number of predators which then got trapped themselves. Put all these together, and we can begin to understand why human and pre-human fossils are rare and individually significant.
Dating may use strata for initial dating, but only when that strata has been accurately dated by other methods that allow for a sort of "triangulation" or corroboration of dates. For example, radio-isotope dating might give a window of 5,000 years in which an object was formed or deposited, sedimentation and mineral composition may give another range, etc. I'd have to go back into my texts to go over all the methods that are used, but there are quite a few -- not all are applicable for a given time-frame, environment, or material, but most items uncovered are dated using multiple methods. When there is a range of overlap between several methods, that is taken to be strong evidence of the actual date of an item. The actual papers describing these dating tests are not typically published in the popular media, but they are available if you look for them. Typically, popular media and textbooks try to sum up a lot of data received and analyzed from multiple sources and present it as simpler sentences that can be understood by an audience of either students or people with just an interest in the subject. They are a "digest" of sorts, but they do not represent the actual full library of evidence -- simply because to justify every statement in a "digest" article would turn it into an encyclopedia. But the information is out there if you wish to investigate it further yourself.
I don't think there are any "fossil humanoids" that are 20 million years old -- that's over 3 times older than the proposed split between the chimpanzee ancestors and human ancestors. Most of the "pre-human" fossils differ from "pre-chimpanzee" fossils primarily in the anatomical changes related to walking bipedally -- there wasn't much of a difference in brain size until much later.
The earliest fossils of "anatomically modern" humans are only about 200,000 years old. The oldest evidence of "art" is about 75,000 years old (pierced shells -- cave paintings go back I think to about 40,000 years ago). The oldest evidence thus far of agriculture is only about 10,000 years old. What this implies is that while according to fossils, humans "looked" like us 200,000 years ago, further changes must have been continuing to occur in how they were able to think. Behavior and cognition do not get preserved in the fossil record -- they must be must be inferred and interpreted by archaeological remains of things the individuals made, did, or left behind.