In real life, a mounted knight was the medieval equivalent of a tank. A few dozen trained knights could defeat an army of thousands with a well timed cavalry charge or flanking maneuver.

Why? En masse, a disciplined army could overwhelm mounted knights. But most medieval armies consisted primarily of hastily assembled untrained feudal peasants pressed into service by their lords. These were not professional, disciplined soldiers. Nobody wants to be roadkill when that charge hits so the front lines would falter. Once a few men turn and run, everyone else quickly follows. The battle turns into a route with the mounted knights slaughtering the panicked opponent. Many engagements lasted less than an hour.

Look at that screenshot from Battle of the Bastards. According to the GOT script, there were 2,000 Knights of the Vale who encircle and overwhelm the Bolton army immediately. This was Season 6! You are telling me that creepy breastfeeding lady in the Vale was sitting on a super weapon this whole time?…