It's a matter of odds. There's a reason why professional warriors such as knights and samurai favoured grappling as the unarmed portion of their arts.
Yes, a good Muay Thai fighter can KO a wrestler. However, if he doesn't, he's in serious trouble. As a striker, you only get one good chance to deal with a grappler trying to close with you. The grappler, once close has say two or three chances to grapple you before you can reset range or land a sweet elbow. If he's good at throwing you get hit with a planet. Ouch.
There are no absolutes though, as we've all seen. Sometimes grapplers get knocked out. Sometimes strikers get submitted or broken by grapplers.
In short, bet on the grappler over the striker, but don't bet your house on it.
The first part is a common misconception. The reason armed, and often armored, warriors and Knights used grappling unarmed arts isnt related to any inherent superiority of grappling, a good unarmored/armed striker can deal with a good unarmored grappler. The reason can be anwered by answering the following questions.
1. Which makes more sense. Striking at an individual armed with a weapon, who will use that weapon to parry your strike, or grappling with them to minimize or even remove that weapon from the equation.
2. Does it make more sense to punch, kick, elbow and knee a person wearing armor, or to use grappling techniques that allow you to damage the joints which can still move, and be moved, due to the articulation of the armor?
Striking is not necessarily about getting a KO. Via striking in a real fight you can have a fully conscious opponent that can't do crap. A kick to a knee that sheers a knee cap and/ or hyper extends the joint, broken clavicles, legit broken ribs (not fractured). With proper striking techniques, using leverage principles, you can hyper extend elbows and with proper striking you can even have a fully conscious guy who simply can't see for crap, not because their eyes are swollen shut alla Rocky but because there are strikes where you directly hit the eye. There are so many things that can be done.
Additionally few traditional martial arts are pure striking. Even Wing Chun, which is seen as a stereotypical striking art, has Chin Na involving wrists and elbows.
As someone else noted the main issue is that a lot of strikers and even some striking arts in particular are simply not good at applying maximum force once a grappler gets inside a certain range, however that is FAR from universal.
and if you were a member of those classes you were entitled to carry more than just a knife, unlike the commoner.
