It’s interesting that a lot of people think medieval knights were slow due to their armor. In truth full plate armor weighs no more than a modern soldiers pack, and being spread over the entire body is not much of a hindrance to movement at all. Knights fought equally well on foot or horseback.
I have made and worn chain mail and plate. You are correct, is is not as bad as many think it is. The SCA (society for creative anachronism) conducts fights in all forms of armor recreated from history.