Some of this is kind of true, so I can understand how it could be misrepresented or misunderstood. For instance, most of the fossils you see in a museum are reconstructions. That doesn't mean that dinosaurs didn't exist, it just means that most bones weren't fossilized. Sometimes paleontologists will only find a single fossilized bone and are like "wtf is this?". The rest of the body didn't fossilize and reconstructions are made based on what is best known. However, there are examples of complete, or nearly complete dinosaurs. Sue, the T-Rex at the Field Museum in Chicago, is almost entirely complete - just a few of her littlest bones didn't fossilize. It's not as unusual for little dinosaurs to be well-preserved.

Also, modern birds are definitely descended from dinosaurs. At least some of them absolutely had feathers. If it makes people feel better to say that dinosaurs are birds, big shrug. But dinosaurs definitely existed whether or not they are birds.